Not defending google, but
Microsoft is neatly ignoring the fact that it's P3P implementation is flawed at best, and causes web developers issues between different IE browser versions ( no surprises there ).
Specifically, IE will refuse third party cookies within iframes, and will show a warning message regardless of your privacy settings.
This makes it a pain for social application or widget developers - the workaround being to invalidate the P3P string entirely forcing IE to accept all cookies from your domain.
Facebook do the same thing as google, setting their P3P header to:
P3P: CP="Facebook does not have a P3P policy. Learn why here: http://fb.me/p3p"
No doubt google and facebook are mainly concerned about protecting their metrics and ad tracking business.