But there is a problem in that the App Engine is not Open Source, or is it? So to move one's site to EC2, a lot of reprogramming would be necessary.
Along these lines, it strikes me as odd how people that would want to run open-source software on their own computers are completely content with running closed web applications where they have no freedom and no control at all. It may be the same reason people are willing to pay for bottled tap-water: convenience - it seems to trump other factors (including ethics and morality) by far.