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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.I haven't read every report and break-down of their earnings because  It doesn't concern me.  It's none of my business.  Reading such things bore me.
It might just be a server under maintenance.....