Why is that ? because the Adwords team just did an update on the landing pages quality factor.
Graywolf goes deeper and diggs some issues.
As an end result, with a lot of landing pages getting a lower score, and with the increasing minimum bid per keyword/keyphrase, Adsense publishers should notice an increase in revenue.
Update: At Threadwatch, Graywolf shows you (on his own skin) a practical example why your Adsense earnings will increase.