The longer I look at the situation, the more I'm coming to the following conclusions:
RG3 is a terrible QB mechanically. He consistently has wrong/poor footwork, can't read a defense, can't prep the offense at the line, and doesn't go through his progressions well.
All the BS last year about the coach and others piling on him for his poor play WASN'T specifically because he was causing turnovers or missing open guys, it was because he was doing all of the things I mentioned above (and was also turning the ball over, taking sacks, etc...)
Through a couple preseason games this summer, it was pretty clear that had had not improved (at all?) enough to be a viable NFL QB.
Cousins does all the little things right. He aligns the team properly, he can read a defense at the line and make adjustments, his footwork and mechanics are good. He's just not a great talent. He's capable of working within a fairly limited set of constraints and produce good results sporadically. About once every 3 games...
From my perspective, I don't see this as the media giving him a pass because he's white/the backup/not RG3. He's getting properly skewered for some very poor decisions this week, but from a (mostly) unbiased perspective, he's pretty clearly the best QB on the roster warts and all.
RG3 had all the problems listed above, AND he's a giant media/endorsement whore, AND he appears to have lost the locker room, AND he hasn't dedicated himself to the finer points of becoming a quality NFL QB. Add all of this to the on the field problems, and he has 100% deserved all of the bashing that he's taken in the press over the past three years.
People have compared the criticism that Gruden laid at his feet last year and the relative praise he's given Cousins this year as proof that the coach hates Griffin. While this may be the case, I don't think it was "wrong" per se. He shouldn't have come out and said all that to the press, but he was terrible at press conferences last year. He's learned from his public relations mistakes and isn't taking that tack this year. So at least there's -some- growth that Gruden has shown.