Some authors can do experienced, worldly women who are also vulnerable for the right alpha male. Lora Leigh comes to mind. She does alpha heroines combined with alpha heroes. HOT stuff!
But DP is all about nice girls who find themselves attracted to testosterone-laden alpha males and can't begin to imagine that he would be attracted to her. I think that one reason her books are so popular is that most of us can relate to the heroine. We can remember being young once, doubtful that we could ever attract the attention of the captain of the football team. We love the fantasy that under all that beefcake and self confidence, he's a vulnerable, sweet guy, tired of women who demand his attention as their due. He wants that shy, quiet girl who would appreciate being the center of his world, but never expects it.
I do occasionally want to reach into the pages and strangle the heroine for tolerating the hero's attitude and not standing up for herself. But to do battle with him would not be characteristic for a woman who has never been bullied before. It makes it that much more fun when she finally reaches the breaking point and gets in his face. It blows our macho hero right out of the water.
Another atypical DP: Regan's Pride
Also not to be missed is Rawhide and Lace