That's a good point. I think Google recognizes the value their cloud platform brings to early startups and wants to put their fears to rest about costs (at least the initial $100k).
But startups could easily use AppScale to move off Google and on to AWS/Digital Ocean etc. when they start to get real traction or when the free credits run out.
Agreed! AppScale is one option for GAE-oriented folks, or running using any of the obviously platform-agnostic methods (docker, mesos, for that matter chef, puppet, ansible, saltstack...).
But startups could easily use AppScale to move off Google and on to AWS/Digital Ocean etc. when they start to get real traction or when the free credits run out.
http://en.wikipedia.org/wiki/AppScale