Your argument is exactly why I don't use Google AppEngine. I know there are open-source stacks now that you can use if you want to take your AppEngine code in-house, but trying to build up an AppEngine infrastructure at probably the worst possible time ("we're getting billed @ $10k/month, but only making $8k! getting more popular will cause us to lose more money! quick, switch to custom servers!") when you can build up a solid infrastructure using technology that you can replicate on any VPS or managed box or colocated hardware that you buy seems the easiest way to scale.