Any why not ? Do you think that Google only receives its money from adverts that appear on sites ? If so, think again.
Q1 2012 had +20% revenue from the partner sites (display network) alone - which is just a part of Google's total revenue.
Adsense observations on this board and elsewhere seem to indicate a decline - not to mention a surge in banned accounts.
My thought is; Would it be wrong to expect a decline in Google's Display Network revenue for Q2 (iso +20%) with the much tighter click validation? The endless talk about the effects of a 'valid click' and 'traffic quality' would only hurt publishers and not Google?