A great example of begging the question. The basic assumption is that Google's UIs are unpopular without any evidence that this is true; given the wide popularity among the people I know (even the designers) I think it'd be more accurate to say that Google is successfully producing clean, functional designs and not even attempting web design contest entries.
UI is more than looking pretty - gmail is popular because it stays out of the way and lets you focus on content, which it handles quite well; in contrast, iTunes increasingly feels like a train-wreck because they swap icons without fixing any of the quirky behaviours and non-standard interface conventions which users must memorize. It was also a confusing comparison because a UI for managing a tightly-curated, highly-structured list containing on average a few thousand items pre-selected by the user isn't obviously relevant to arbitrarily searching across billions of unknown items.