I think the main difference between Manning and Romo (and all other QB's) is that Manning knows where the ball is going before the ball is snapped. Not every single play, but the majority of the time. So he doesn't have to go through progressions. He sees his guy and throws it, giving the d-line no chance to get to him. Meanwhile Romo typically goes through his reads, which gives the d-line more chance to get to him, especially when there is a shaky line in front of him. It has little to do with his release, but more to do with the fact that he has to go through progressions, which Peyton doesn't do often. He knows where the ball is going, he just has to wait for his receiver to separate.