Salepriced, I'm pretty sure you are wrong here. You're not getting it:
People's AdSense earnings going down could mean everything. If the PRICE of keywords was going down, though, then that would be a matter of concern.
If you have 1000 people with Adsense accounts who earn $1000 a month one quarter, and then 2000 people who earn $600 in the next quarter, GOOG earnings are still up. I have both AdSense and AdWords accounts, and haven't noticed any negative trends.