Concerning Aladdin, I do remember there being a minor uproar over a lyric that went along the lines of "they'll cut off your ear if they don't like your face, it's barbaric, but hey, it's home." And there was, in fact, some discussion in Muslim communities over Jasmine's lack of a veil. Ultimately it wasn't a huge deal.
The Milly-to-Tiana switch occurred because the character was originally supposed to be a house cook. There was a bit of a negative reaction to that, so they switched it up. I imagine they changed her name because Tiana sounds more "princessy."
Anyway, your overall point. It's a big deal simply because there hasn't been a black "princess" before. This is significant in the same way Barack Obama is significant, although obviously on a much smaller scale.
In cynical marketing terms, this has a lot do to with the Disney Princess line, which is earning the company an obscene amount of money. All of the characters commonly featured in that line are white. Mulan and Pocahontas are rarely included, and Jasmine (when she is included) is often portrayed wearing more a more
European style of dress. One could make the argument that Disney is trying to make this line more marketable to African American children.
Anyway, it's a kick-ass movie. Definitely a return to form for Disney after years of sludge.
