I hate to say this and it isn't nearly on the same scale, but I think it's sort of comparable to the shooting in Norway last year. Yes, the media at large condemned the action, but not the motivation behind it, because a huge number of people implicitly agree with it. "We don't want nasty foreign brown people here!" is a sadly common sentiment, no matter where those "brown people" are from or what religion they may belong to.
Americans as a whole tend to lump all non-Latino "brown people" into one entity, and almost every article notes that Sikh men wear turbans and are "easily confused with Muslims." So I think there's a significant chunk of the population who agree with the apparent motivation, if not the action and the fact that the shooter managed to get the 'wrong' group of people. This opens another can of worms. I don't want to imagine what would happen had the target been a mosque rather than a Sikh temple.
The other reason I can think of for the outpouring of expression of shock and grief over the Aurora shootings is that for most people, that could have easily been them. In this case, if you're not a minority from certain ethnic backgrounds, you're safe.