There were 19 different instances of a passing play netting 20 or more yards against the Redskins in just the last 7 games alone, according to the Football Outsiders game charting data. Here's the breakdown:
1. H.B. Blades vs. Jason Witten, 28 yards (5 rushers)
2. Carlos Rogers vs. Terrell Owens, 25 yards (5 rushers)
3. Chris Horton vs. Martellus Bennett, 25 yards TD (4 rushers)
4. Shawn Springs vs. Bobby Engram, 21 yards (4 rushers)
5. Fred Smoot vs. Amani Toomer, 40 yards (5 rushers)
6. Kevin Boss uncovered vs. all out blitz, 24 yards (7 rushers)
7. Derrick Ward slot screen, 48 yards (4 rushers)
8. Derrick Mason hole in zone, 26 yards (4 rushers) [Horton credited with tackle]
9. H.B. Blades vs. Todd Heap, 30 yards (5 rushers)
10. Todd Heap on trick play (TE falldown), 24 yards (5 rushers) [D. Hall credited with tackle]
11. Carlos Rogers vs. Derrick Mason, 28 yards (8 rushers [!] [why?!])
12. DeAngelo Hall vs. Chad OchoJohnson, 23 yards (4 rushers)
13. Cedric Benson RB screen, 79 yards (4 rushers) [Rogers credited with tackle]
14. Shawn Springs vs. Chris Henry, 22 yards (4 rushers)
15. Lorenzo Alexander vs. Brian Westbrook...47 yards (3 rushers)
16. Chris Horton vs. Billy Bajema, 29 yards (5 rushers)
17. Rocky McIntosh vs. Michael Robinson, 24 yards (5 rushers)
18. Fred Smoot vs. Josh Morgan, 26 yards (4 rushers)
19. Shawn Springs vs. Bryant Johnson, 24 yards (6 rushers)
I added the number of rushers to put into some context the coverage. In 6+ rusher situations, the Redskins are always man-to-man across the board, sometimes with a deep safety, but always man. In 4-5 rusher situations, they could be playing either.
It's worth mentioning that the Redskins recorded neither a hit or a hurry on any of these plays. That doesn't tell us very much, since you'd expect the average pass that was completed for 20+ yards to be done in favorable LOS conditions. Even if the Redskins increased their hits and hurries on the QB, there's no reason to expect this trend to be any different.
We can draw a few conclusions for this. Neither DeAngelo Hall nor Carlos Rogers really had a hand in the downfall. Rogers was beaten once by Owens, Hall once by Ocho Cinco, and it's hard to blame Rogers for the Mason TD when an 8 man blitz gives the quarterback enough time to let his receiver execute a double move. Then you have a bunch of "their scheme is better than our scheme" big plays, and two well executed screens that are a knock on the reads of the front seven.
Once you eliminate all the noise, you are left with a handful of big plays against Smoot, a handful of big plays against Shawn Springs, and a few bad reads/missed coverages by Chris Horton. Smoot and Horton return this year, and it's hard to imagine a rookie Kevin Barnes being any better than Springs was last year as a rookie. Considering that Greg Blache is just as likely to draw up some bizarre defensive schemes this year as he was last year, the Redskins propensity to give up the big play is unchanged from the end of last season, when they were doing so about three times a game.