Unless you selected a platform that is too complex to start with. I think that many of the PaaS companies I see today are here mainly for two reasons: Rails & J

Unless you selected a platform that is too complex to start with. I think that many of the PaaS companies I see today are here mainly for two reasons: Rails & Java frameworks. Can't speak for Heroku but with EC2 you get the ability to dynamically add/remove instances. While this seems like it's needed only for certain kinds of startups, the reality is that most background processing is batch oriented and it's extremely cost effective to just spin up instances when I need them, crunch the data and terminate them after that. And, if you go for spot instances (and use a fault tolerant framework like Hadoop to distribute jobs), it's becomes even more cheaper.