I guess there is more to someone than appearance and talent. Gwen is an all around kind, fun, and genuine person (yes I have met her) with a very good heart. Which balances out maybe the perception that her talent is lesser than Miranda. But keep in mind that Gwen has more going on than just music... She is a brand.
Miranda's behavior and then sad antic at the awards show with her song just emphasize that she seems shallow and petty.
Even the most beautiful person can be unattractive with a crappy attitude. And conversely the right attitude can make a mediocre person more attractive.
And yes, Gwen has been doing too much to her face but she still looks great by the standards she is being held to in her position. I am sure there is pressure for her to continue the work on herself as she approaches 50 so long as her image and brand are marketable. I do look forward to when she can sit back and age a little more gracefully.