This is incorrect. AdSense was 31% of their revenues in Q409. They did more than $2B in AdSense revenue in Q4 alone:
http://investor.google.com/releases/2009Q4_google_earnings.h...
http://investor.google.com/releases/2009Q4_google_earnings.h...
Those numbers are net sales, not gross revenue, so cost of revenue (revenue splits, traffic acquisition costs, etc.) are factored out.