I had forgotten about the pass to Vereen that started this avalanche. Re-watching that sequence, it would be interesting to know what the call was and what Bart Scott's responsibilities were on that play. Collinsworth might be right that there was a planned "rub" by Welker, but it also looks like Scott was trying to provide coverage if Welker broke his route off short.
If that was the plan - Watch Welker short, if that doesn't happen, cover the back out of the backfield - then that was a poor idea considering the speed disparity between Vereen and Scott. At the point Vereen catches the ball, he's about halfway between the numbers and the sideline and Scott is still inside the numbers. If they ran that play again and Scott completely ignored Welker and went straight for Vereen, I'm not even sure if he gets there in time. Maybe he'd be able to dive and push Vereen out of bounds, maybe not.