It's not my argument -- it's Mangini's, who was on the defensive staff. And he's saying explicitly that the Rams helped the Pats by not running. I suspect the reason the Rams were able to finally move the ball in the 4th quarter is because the defensive line started to get worn down and perhaps Martz started to better understand how to attack the coverage.

But it's pretty clear that the Patriots' defense was designed to defend the pass at the expense of the run, and the Rams didn't take advantage of that, whether it's because they wouldn't, or they couldn't.