And Search exists basically to supply inventory for AdWords. They wouldn't have anything to run ads on without search (okay, not quite true, there's AdSense, but they wouldn't have developed either...)
But yeah, that merely proves my point. If click-throughs started to drop, what other money making products does Google have in its portfolio?
(don't get me wrong, I love and use Google products as much as the next fella, but I also understand that their search/ad revenue is what's subsidizing my use of Google Earth or Picassa or whatever)
For example, Google Earth does some actual business business, and probably makes a bit of cash selling pro versions and geospatial servers and services (haven't looked at the 10-k to be honest). Orkut, Sites, Knol, Chat, Wave, Scholar, etc. does not.
Some things like SketchUp are designed as loss leaders like Search to provide content to things that might have a decent revenue stream like Google Earth (except most of the paying users are probably not using the Sketchup Data).
But other, more expensive things like Chrome and Android have a link to making money that's very tenuous at best.
And we also already know that Search Ads account for 99% of Google's revenue stream. Subtract that out and we have a very good idea of where Google's other offerings are.