Publisher - 5:16 pm on Jan 11, 2006 (gmt 0) Just my 2 cents
I'm pretty new to this stuff but is it possible that Google rotates all ads to be sure that all ads get some exposure? It would make sense that if 10% of the ads pay the most, the likelihood that the remaining 90% would get shown more often. This likelihood would show up as decreases in earnings because you're showing the lower bidded ads more often.
Just my 2 cents