1000 petabytes of what? RAM? How do you know that's enough to do what you want anyway? My point at any rate is that we can't grab a billion dollars and make some computer that is "fast enough to 'evolve an AI'" just by throwing money at the problem - universities, companies and governments are spending money right now on supercomputers, and they still have limitations due to underlying technical issues like cooling and inter-processor communication (as the other commenters pointed out).

Watson is a big complex program, not some small DNA-like seed that can easily be mutated and iterated on automatically. There's no known small seed that generates anything like a general intelligent agent (except of course DNA itself and the resulting biology which can't be very efficiently simulated even with a supercomputer).