I might be wrong on this, but I think if you have an injury inside 2 minutes and no timeouts -- and you're losing -- then it's a penalty. Does this sound familiar to anyone else? What made the NE ploy (if it was one) interesting is that they were ahead but needed to slow things down, since Manning was just throwing at will against them. That's an unusual situation.
My first thought when Ty Law was limping around at that same time was that he's just trying to draw the throw on the next play. It just looked too obvious. Or maybe there was some mixup about which player was supposed to be 'injured.'
In retrospect, it's probably too bad for the Colts that they got the ball down to the 2-yard line. If they'd needed to score from the 8, Manning probably throws a TD. The Pats looked hopeless against him.
I think you're right though: even if the injury was legit, if there's no way to stop it with the rules we'll see it again at some point. It's not often you have a lead late and want to stop the clock, but it's bound to happen.
Removing the injured player for the rest of the half is an interesting idea, but it might be overkill.
Here's another one, that won't solve the problem but would limit the ploy's usefulness a little: you cannot make any substitutions except for the 'injured' player. No changing your DF package, no fresh DBs, etc.
