I'd be surprised if that happened. Google will only remain the market leader while the perception is that their search results are better than the competition's. Selling them out (and Yahoo are already out selling Top 6 SERPS slots incidentally) would be a dangerous strategy and I'm sure they are fully aware of that. Unless they feel that their product range is now so vast and inherantly embedded that they can survive such a change.
The colour they have chosen suggests to me they are "trialling" the blur between paid and unpaid to see what the effects are.
[edited by: Simsi at 5:04 pm (utc) on May 1, 2008]