Pertaining to your theory:
If male teenagers were voting, don't you think Pia would still be on Idol? I presume teenagers means girls. 
I don't think male teenagers would be voting for her, if they vote. Her image is too mature and polished. I think these teenagers would vote for their own - image-wise, that is.
PS I do think that Gwen's style works only for Gwen; the style looks atrocious on other women with non-Gwen body types (hated Lauren's outfit). I think it would have helped Pia to have gone for "younger" outfits (if she wanted the teen vote) and not always for a decked out Celine-style wardrobe. The perfect opportunity would have been Rock week. Also, the judges did not help her any by giving her a pass for staying in her own little bubble up there and not working the stage. I think Pia is more of a "glory" than a "grit" singer. So I wasn't quite on board with her rendition of that Tina Turner song. For me, what was always missing in her performances was a connection with the audience. I sit there, listen, and admire her but never really get involved in her peformance. I feel like a spectator and after a while, her performance becomes very boring for me. I kinda understand how she got voted off, though I was not expecting it (didn't think my reaction to her was typical of the AI audience, plus there were worse performers in the group).
Hop (and anyone else who is interested), if you listen to Celine Dion's version of "River Deep Mountain High" you will know where Pia got her version from (it is on youtube - I've included a live version. PS...Although, I love Celine and she is a true performer, I do sometimes think she is a little "cheesy"). Celine however, has learned how to PERFORM. Pia hadn't learned that yet (maybe she won't?).
More important to her demise, I think, is her lack of an emotional connection. If you watched her (Pia) on Idol, she was very restrained with her emotion...even when she was told she was eliminated, she held back her tears and her emotion (maybe it was shock) for a long time. That withholding of emotion came across in her singing. If she can learn to let go and really connect emotionally to the song and to the audience - as someone (MD) we all created this forum for, who just feels it in her bones - then she (Pia) "could" be a great star with that voice, her sweet disposition and her looks. JMO
By the way... I think there is one female vocalist who taught herself how to perform a song through her own inner demons and emotional pain and her desire to be an actress. Of course, you know I refer to Barbra Streisand. Ms. Doolittle also has the same, what is IT?, emotional connection to both the song and the listener. The emotional connection and performance ability and style they both innately have just makes you FEEL them SING. Here is my favorite Barbra performance to prove my point (of course, it is subjective about Barbra and is just my own opinion, but we are all here because of Melinda - so you get what I am trying to convey - PERFORMANCE & EMOTION are what we all want when we listen to and watch a vocalist) Oh, and we want to have FUN too, don't we?
Sorry for getting off track...
HAPPY BIRTHDAY, MOMMY M! YOU ROCK!