I'd like to address a couple of points you made here, cause I don't necessarily disagree with you but I think I have a different conclusion:
he fakes a cramp, nobody would be saying anything here. - Agreed
Receivers do tap themselves es out of a play usually after a go route they run - Yes, this happens
I think the main thing you have to consider is that the QB is the leader of the team, he is not just another player and is held to a much higher standard. He is expected to model behavior for the rest of the guys, including mindset, toughness and discernment. I personally have never seen a QB take himself out of the game, especially not at a crucial moment in the 3rd quarter. That's not a winning mindset, especially as a leader of the team. His honest response that he took himself out was pretty poor discernment - he should have known how bad a look that was, the fact that he didn't shows a lot of ignorance and definitely a lack of discernment in how to handle himself in front of the media. Watch Kurt Cousins screaming in pain from hits last year and still limping to the huddle, this makes guys want to play for you. Zero modeling of toughness tapping out of a drive as a QB. I don't think you realize the poor effect this has on a locker room.