Well the revenue share from AdSense was revealed to be in the 65% range. So given a poor profitability by Google in the next few million years, it could still work.
http://adsense.blogspot.com/2010/05/adsense-revenue-share.ht...
it's 68%. Wow, I wasn't expecting google to pay out quite so much.
At those percentages it actually becomes possible. Depending on how profitable the sites and Google are at serving the content and the ads (respectively) it could work.