The media likes an easy to understand, prepackaged story. There's the good guy that is virtuous to a fault and, hopefully, there's someone around to assign the role of bad guy who is without any redeeming qualities.
They don't like that story to apply to more than a few people and, ideally, applies to one good guy and one bad guy. With the QB the most visible position by far, he makes for that nice, easy to tell, prepacked story telling. The media also don't like the story to have too many details/nuances to explain. "It's a team sport and a team win" is a platitude that just won't sell as well. They want a story that is the good guy leading his team by exemplary play, behavior and attitude. Anything that doesn't fit that will be conveniently unmentioned or swept aside.
In fairness to Manning on this one, as TB/the Patriots learned in 07, no matter how potent your passing offense, when your OL can't keep the opposing DL from an almost constant pressuring the QB, your passing game is going to flounder. What we saw in yesterday's SB was Manning having to throw without the benefit of timing (something he is master with). His throws were uncomfortable and forced based largely on pressure. If the Seahawks DL would have pressured him much less (a la Patriots two weeks ago), Manning probably would have put up plenty of scores. Enough to win? Who knows...