i think it's all a hoax that she writes her own stuff, or at least, these whiz bang producers take her base songs and make them into fully produced songs with slick instrumentation and arrangement etc. there's also the way she has been marketed as a "punk kid" with that ridiculous tie deal, especially when she's a suburban chick from canada. Avril doesn't have much of a voice or guitar skills. you can't deny that.
yes, they are all production, even aguilera, who is the only one that has super talent, as in her voice. jessica simpson has a decent voice, but one would hardly call her really talented, imo, beyond her ability to play the blond sex bimbo to a T (which i guess like britney and her catholic schoolgril shtick for a while is some sort of talent, though not musical)
and yes avril is a much tamer version of alanis, a completely ripped off version if you ask me, which is why she seems so derivative imo.