There is some merit to this. There are a lot of DBs in the league who can "cover", in other words be next to the guy they are supposed to defend, Darrius Butler is a case in point. What separates THOSE guys from the elite CBs is the athletic ability to make a "play" on the ball when it gets there.(knock it down or pick it) And by that I mean the ability to find the ball, and NOT have your back to it, like we see so much of. The ability to time your leap at the proper moment. The ability to anticipate the QB and jump routes.
There are 2 other points I'd like to mention in McCourty's defense. First is the old, but true, "zone" defense. When your job is make sure no one gets behind you, passes are going to be completed in front of you.
The other point is a bit more obscure. Last Monday, Henne dropped back 49 times. IIRC (and I could be wrong) I read where McCourty was targeted 10 times. Then it brings the question to mind that if McCourty was covering Marshall the other 39 times then he must have been doing a pretty good job, because IF he'd been open those other times, what QB wouldn't have thrown him the ball. Ergo McCourty must have been doing a very good job those 39 times. vs the 7 or 8 balls that he caught
Well we know that McCourty didn't cover Marshall one on one on every play, and we know that Marshall couldn't ahve been the main target on every play, BUT the point remains. As fans, we tend to focus and judge DBs on those times the ball is thrown in their direction, and ignore those times their coverage is good enough to discourage the QB from throwing at them.
Clearly it wasn't McCourty's best night, but given who he was playing, and the fact he wasn't being beaten soundly. He WAS there. But on this night he didn't make the plays on the ball - (his dropped pick being exhibit one, his missed strip at the one being another)
I'm not worried a bit about him. He's one of the better CBs in the conference. Lets give him a bit more time to develop into what he will become.