I looked at about 10 of these that I hadn't seen before, and they're all either google-foo projects or their developers have @google.com email addresses.

While that's certainly true, is there an item in he linked that serves as an example of such a non-google project?

I thought it was odd that they would omit Guice, Gin, and GWT from a list that includes Android and Chromium.

The 'google' tag for projects on Google Code is privileged, and all officially sponsored ones use it: http://code.google.com/hosting/search?q=label:Google

There is a higher level for official Products and hosted APIs where there is a full-fledged team behind it and a much higher level of support. Instead of being labeled projects, they have top level sites:

  http://code.google.com/appengine/
  http://code.google.com/webtoolkit/
  http://code.google.com/projecthosting/
  http://code.google.com/apis/wave
  http://code.google.com/apis/gears/
  http://code.google.com/apis/adwords/