NFL.com is actually searchable for this. Here are the WRs drafted in rounds 4-7 for the prior 4 years -

2009
4 107 Mike Thomas WR Arizona Jacksonville Jaguars
4 108 Brian Hartline WR Ohio State Miami Dolphins
4 124 Louis Murphy WR Florida Oakland Raiders
4 127 Austin Collie WR Brigham Young Indianapolis Colts
5 140 Johnny Knox WR Abilene Christian Chicago Bears
5 141 Kenny McKinley WR South Carolina Denver Broncos
5 144 Jarett Dillard WR Rice Jacksonville Jaguars
5 160 Brooks Foster WR North Carolina St. Louis Rams
6 175 Quinten Lawrence WR McNeese State Kansas City Chiefs
6 194 Brandon Gibson WR Washington State Philadelphia Eagles
6 206 Dominique Edison WR Stephen F. Austin St. Tennessee Titans
7 224 Demetrius Byrd WR Louisiana State San Diego Chargers
7 229 Manuel Johnson WR Oklahoma Dallas Cowboys
7 232 Julian Edelman WR Kent State New England Patriots
7 233 Sammie Stroughter WR Oregon State Tampa Bay Buccaneers
7 243 Marko Mitchell WR Nevada-Reno Washington Redskins
7 251 Derek Kinder WR Pittsburgh Chicago Bears
7 252 Freddie Brown WR Utah Cincinnati Bengals
7 253 Tiquan Underwood WR Rutgers Jacksonville Jaguars

2008
4 105 Will Franklin WR Missouri Kansas City Chiefs
4 106 Marcus Smith WR New Mexico Baltimore Ravens
4 125 Arman Shields WR Richmond Oakland Raiders
4 126 Lavelle Hawkins WR California Tennessee Titans
4 128 Keenan Burton WR Kentucky St. Louis Rams
5 136 Kenny Moore WR Wake Forest Carolina Panthers
5 153 Matt Slater WR UCLA New England Patriots
6 171 Marcus Henry WR Kansas New York Jets
6 174 Josh Morgan WR Virginia Tech San Francisco 49ers
6 182 Kevin Robinson WR Utah State Kansas City Chiefs
6 191 Paul Hubbard WR Wisconsin Cleveland Browns
6 193 Jaymar Johnson WR Jackson State Minnesota Vikings
6 205 Pierre Garcon WR Mount Union Indianapolis Colts
7 215 Justin Harper WR Virginia Tech Baltimore Ravens
7 217 Brett Swain WR San Diego State Green Bay Packers
7 224 Steve Johnson WR Kentucky Buffalo Bills
7 226 Chaz Schilens WR San Diego State Oakland Raiders
7 237 Adrian Arrington WR Michigan New Orleans Saints
7 246 Mario Urrutia WR Louisville Cincinnati Bengals
7 248 Marcus Monk WR Arkansas New York Giants

2007
4 103 Isaiah Stanback WR Washington Dallas Cowboys
4 118 Ryne Robinson WR Miami (Ohio) Carolina Panthers
4 128 Chris Davis WR Florida State Tennessee Titans
5 142 Steve Breaston WR Michigan Arizona Cardinals
5 146 Aundrae Allison WR East Carolina Minnesota Vikings
5 157 David Clowney WR Virginia Tech Green Bay Packers
5 169 Roy Hall WR Ohio State Indianapolis Colts
5 172 Legedu Naanee WR Boise State San Diego Chargers
6 188 Joel Filani WR Texas Tech Tennessee Titans
6 197 Courtney Taylor WR Auburn Seattle Seahawks
6 210 Jordan Kent WR Oregon Seattle Seahawks
7 227 Dallas Baker WR Florida Pittsburgh Steelers
7 229 John Broussard WR San Jose State Jacksonville Jaguars
7 233 Chandler Williams WR Florida International Minnesota Vikings
7 234 Syndric Steptoe WR Arizona Cleveland Browns
7 235 Chansi Stuckey WR Clemson New York Jets
7 249 Derek Stanley WR Wis.-Whitewater St. Louis Rams
7 254 Johnathan Holland WR Louisiana Tech Oakland Raiders

2006
4 103 Brad Smith WR Missouri New York Jets
4 104 Cory Rodgers WR Texas Christian Green Bay Packers
4 109 Jason Avant WR Michigan Philadelphia Eagles
4 111 Demetrius Williams WR Oregon Baltimore Ravens
4 119 Brandon Marshall WR Central Florida Denver Broncos
4 125 Skyler Green WR Louisiana State Dallas Cowboys
4 130 Domenik Hixon WR Akron Denver Broncos
5 144 Marques Hagans WR Virginia St. Louis Rams
5 147 Jeremy Bloom WR Colorado Philadelphia Eagles
6 171 Mike Hass WR Oregon State New Orleans Saints
6 172 Jonathan Orr WR Wisconsin Tennessee Titans
6 184 Adam Jennings WR Fresno State Atlanta Falcons
6 190 Jeff Webb WR San Diego State Kansas City Chiefs
6 193 Reggie McNeal WR Texas A&M Cincinnati Bengals
7 218 Todd Watkins WR Brigham Young Arizona Cardinals
7 231 Bennie Brazell WR Louisiana State Cincinnati Bengals
7 233 Devin Aromashodu WR Auburn Miami Dolphins
7 249 Ben Obomanu WR Auburn Seattle Seahawks
7 251 David Anderson WR Colorado State Houston Texans
7 252 Marques Colston WR Hofstra New Orleans Saints
7 255 Kevin McMahan WR Maine Oakland Raiders

That's 78 WRs drafted in rounds 4-7 in the last 4 years. So, that makes it about 5% instead of 1%

but one of your examples was an UDFA I believe (Garcon?). So you would have to include everyone who signed a UDFA contract to the total if you want to include Garcon (unless I'm wrong on his draft status).

Either way it is likely higher then 1% but still not very likely.

But like I said, a reasonable FA signing does not stop you from still drafting players. Just like Bodden does not eliminate CB as a possible 1st round direction.

Garcon was pick #206 (6th round).

I don't expect any UDFA to start in the first 2 years. To me, they are a success if they make the roster. Conversely, I expect to have some production out of draft picks.

Just quickly glancing at the list, what stands out to me is that almost all of the success stories landed in really good situations. Off the cuff, the picks that stand out to me are Collie, Edelman, Garcon, Breaston, Marshall, and Colston. I don't think it's coincidence that most of these guys had either Peyton, Brady, Warner or Brees throwing them the ball. It also doesn't hurt that most got to line up across from Moss, Welker, Wayne, Fitzgerald, and Boldin (and while Colston is the No. 1 WR, he gets the benefit of being one of many weapons to be accounted for). Now, the question is, does Houston, with Schaub and Johnson, offer a similar situation where a late pick could blossom?

That's my point. The answer is yes. :D

I agree that Houston is a place where a late pick could flourish. I honestly feel Schaub is the most accurate passer in the NFL (or at least that him and Brady are in a league of their own). He may not be elite in arm strength, pocket presence, or ability to deal with the blitz, but his throws are more catchable and lend themselves more to YAC then any other QB in the NFL. That is the biggest reason for Owen Daniels' great success. He is a great route runner who gets open, but Schaub puts the ball in spots where Daniels can turn his 6 yard route into a 15 yard gain. Well, that and the fact that 2 players are devoted to AJ and 5 others are worried about him on every snap.

That means a great route runner with sub-par speed who is overlooked on draft day could be very productive here in the same way Anderson has been.

But once you've re-signed Walter, you have no need to draft a WR. You're going to keep five WRs max and we have:

1) Andre Johnson
2) Kevin Walter
3) Jacoby Jones
4) Andre Davis
5) Anderson

plus, we have quasi-WRs in Daniels and Casey.

There's no room for another receiver so you better be drafting a WR very late or as a UDFA. Otherwise, it's a wasted pick.

We were discussing that since we have Walter re-signed, the draft pick that would have been used to replace him can now be used on a different position. My point was that we may have been better off signing a FA at another position that is a "hole" or a "need" and simply drafting a WR in the late rounds.

I wonder how hard it would be to get a FS like Brodney Pool?

The Texans value Walter more than the participants in this thread do because the Texans consider Walter by far the team's best blocker at the position.

They could also be reading Jacoby's tweets this offseason too. ;)
http://twitter.com/jacoby_jones12/status/10209531048

NFLPA reports the base salaries for the Kevin Walter contract as follows:

2010 3,000,000
2011 3,000,000
2012 3,500,000
2013 3,500,000
2014 3,500,000