I can answer that: they aren't interested in advertising and selling the device to consumers. If they were, they wouldn't have been announced at a developer conference. Although oddly, they are advertising the Nexus 7 off the Google homepage.
Do you really think that's so clear cut? I/O has visibility well outside the developer community, it gets covered in the mainstream media. Just today I read about it on the website of the most widely read German news magazine (an article is linked prominently on the front page and it's the lead article in the technology section).
Like Apple, Google can and probably is using their developer conference keynote to announce things to consumers.
