He was obviously hurt. I saw it on that same scamper to the sidelines and he gained about an extra four yards hopping on one foot. But the defense seemed to just lay off. I hadn't thought of the OP's theory before, but reading it now... it makes a whole heck of a lot of sense. Think of one specific situation here... week 1. The Hawks are playing pretty well for a rookie QB in his first game and John Skelton is really pretty much sucking. The team has a good handle on the Cards offense and is keeping it a back and forth game. Skelton is kept in check and is getting worse as the game progresses. He is their first stringer, and after picking up a lot of wins last year, it stands to reason that he is their best option. The Hawks knock him out of the game and Kolb comes in and immediately lights a fire under the team and wins it with a long drive and a TD, because Kolb was healthy and eager to prove himself, and brought a different skillset than Skelton (he is better at staying in the pocket than Skelton, thus Kolb's frequent injuries from holding the ball to the bitter end and getting crushed).
In week 1 if the Hawks do exactly what they did to a hurt RG3 and keep him in the game for the remainder by backing off a bit, then what happens? The Hawks win and are a #2 seed and have a bye Sunday. But by taking out the injured #1 guy and going to the healthy #2 guy who definitely has something to prove and like Kolb has shown that he can play well at times (well, he's done it more so than Kolb so far on a percentage basis.... Cousins looks to be the real deal, Kolb was always "potential"), then you're putting your defense at a disadvantage and risking removing a cold hand with a bum wheel and inserting a potential hot hand with no injury concerns who can do precisely what Kolb did and hit receivers (especially on a tiring D) and turn the game. It didn't happen until much too late, and it only happened because Robert slipped on that godawful kitty litter field while trying to retrieve a low snap. It's not so far fetched if you think Pete is always thinking about the situation and comparing this game to week 1 which was quite similar in that our offense wasn't moving that well for a while and we had AZ stopped cold while Skelton was in, much as we did to RG3 in quarters 2, 3, and 10 minutes or so of 4 before he left. Interesting theory indeed.