Part of it is developmental. There's a certain age when kids are learning about gender differences and are particularly rigid. Girls have long hair, boys have short hair, etc. It's just a way of understanding the world. When they get older, those stereotypes become more malleable.
The other day we went to a water park that has a MagicQuest game. The kids all run around the hotel with wands of their choosing. All the girls who were my daughter's age (5) had the pinkest, sparkliest wand there was, with a sparkly unicorn topper. The older girls were far less stereotypically girly, and in fact, I think they would have found all that pink too babyish.
So I think it's a normal part of development. But yes, the princess movies drive me crazy. I wasn't going to let my daughter watch them at first, but she loves them so much, I gave in. She's not overly girly. She loves worms and getting dirty. But she does love pink too. I figure as long as I'm not pushing the pink sparkly thing on her (as some parents do), and as long as I explain things to her, then she'll be fine.
I don't think Fancy Nancy is bad. I particularly like that they had her playing soccer but her socks simply let her "play better". The new Disney movies are pretty good, I think. "Enchanted" was so funny. But the old ones, well, they're from a different time.