I think there's an element of two-dimensions to three-dimensions going on, as well--which is required in coming from cartoon form into live action. But that may be just me projecting that idea on the film. Going along that line, though, it's not the becoming more cynical part that makes Giselle a more appealing character, it's that she's experiencing a fuller range of emotions, which includes doubt. That said, I think a lot of our Disney princesses in the last few generations had that full array of emotions ready for them. Thinking back, I don't think that full array was available to good old Snow White and Cinderella, who seem to be Giselle's core character models.