I agree to an extent, although I think most people saying that Petrov "doesn't work" mean that he's not compatible in his current position witht he formation we're playing, just like Gerrard and Lampard weren't in England's previous formations under McClaren etc. Now Fabio has changed where and how they play, they're working - just as when we change where and how Petrov plays (ie one of three midfielders), he's more effective.
It's about other players too, ie Barry was added to the Gerrard/Lampard midfield for England, and they blossomed. There's a similar argument here, that NRC should play in a midfield alongside Petrov and Sidwell/Delph/Downing or whoever.