I actually dislike the uber-white, cap all teeth, make sure they're perfectly straight trend; it's like a bunch of stars suddenly have the same smile, in a sense. It's like the botox/surgery trend.
I don't think it's possible to "blame the U.S.A." (like in "South Park" they blamed Canada, lol), but I do think Hollywood has something to do with it. Look at French actesses, like Charlotte Gainsbourgh or Juliet Binoche, or Vanessa Paradis - it seems to me they're all ageing quite naturally, don't have perfectly white, straight teeth, frozen expressions etc.
I'd hate to see that sort of "homogenizing" happen to Alexa; but personally I don't see signs of it yet. I think she's still her quirky self, mixing things up, wearing her hair in her eyes and dried naturally, her swoop of liquid liner, etc. Maybe she has access to more designer clothes now (seems to me she used to wear more vintage) but she still goes for looks that aren't typical, and mixes high and low, masculine and feminine.
At least, imo. Sorry for the long post. Just think it's an interesting side-bar.