http://www.nfl.com/videos/nfl-game-highlights/09000d5d801f96bd/Top-Ten-Mobile-QBs-Donovan-McNabb
The Phillie journos in this video make a good effort of explaining why McNabb (quite rightly) sits in the pocket rather than uses his legs
Did you see Vick the other night? He sat in the pocket and kept his eyes down field when he should and only broke away when it was required, and he did it with aplomb! This is a different Vick to what people saw at the Falcons, he's matured a lot on the field, he's a QB first and a 'RB' second, not the other way around.