Because Belichick constructs vile mean spirited defenses, and believes in a ball control offense that will leave Manning sitting on the bench for a lot of the game. He might still get 3 TDs, but most importantly he probably won't get enough TDs to win. Belichick is perfectly happy giving up 70 points, so long as his team gets 71, that's the way he coaches (just win) and that's what his team has been doing for him since he took over.
Now I'm totally confused... I thought we were talking about the Rams and Falcons?
In all the anlaysis of tomorrow's Pats-Colts game I have yet to see one show break down the Pats offense vs. the Colts defense.