Even though initiatives like EC2, S3, wikia and nutch are lowering the barrier for the next wave of innovation on search - building and maintaining an internet wide index is still a huge engineering initiative.
The only player which comes close to google is yahoo. If yahoo opens up its index like wikia it could set the stage for the next wave of innovation in search. Through a use based pricing model like amazon it might also make business sense for yahoo (lets face it, yahoo search isnt really going anywhere yet) and just might also help yahoo in getting its mojo back.
I'm much more comfortable with building applications on top of infrastructures I pay for instead of being held hostage to the odd loyalties and uncertainties that come with ad supported services.
I may want to be yahoo's customer but I don't want to trick my own customers into somehow watching yahoo provided ads or rely on some other indirect means of helping them make money.
Amazon does the right thing. I hope they succeed.