Now if they all threw 100 balls Leinart might make 5 more, and Jay 7 more than Vince. I'm not seeing that it's a huge difference personally. Just think there's a whole other dimension to Vince that the other two don't have and it's not like they can work on it, but Vince can work on passing (which he has been doing).
It's not a huge difference. The difference is what happens with those extra couple of completions. It just gives Leinart and Cutler more opportunities to make a big play.