Nice post. It is important to note that these tend to be cyclical. As start-ups go through various stages of their life cycle, PaaS/ IaaS providers update their offerings and technologies mature/ invented, the appeal may shift between these options. I think it makes it even more important to build your technology stack in a way that is:
1) easy to deploy, migrate and update (using standard deployment technologies)
and
2) least dependent on a specific vendor (GAE ;)
1) easy to deploy, migrate and update (using standard deployment technologies) and 2) least dependent on a specific vendor (GAE ;)