The idea behind ey-solo(and the soon coming ey-flex) is that you don't want to have to learn all that stuff. We have been running and managing high volume ruby apps in production for 2.5 years now and we have taken our whole battle tested stack and are now offering it as SaaS.
So the goal is to save you time and hassle. We will maintain the whole stack with constant feature and security updates as well as bug fixes and all you need to do is write your app and leave the deployment and scaling hassles to us.
AWS is only the beginning, this platform will soon be available on other clouds as well as be downloadable so it can be run on any hosting provider if you run our linux and install our agent.
This means that eventually you will be able to host anywhere and still use our automated stack to manage the servers.
given my experience with slicehost, basic sysadmin isn't hard to learn; not to mention if you're using rails there's the deprec2 gem that can do most of baseline sysadmin tasks (if not all of it for you)
I agree with another post; something like heroku (with extras) is more desirable or a more economical rightscale
bottomline: not cheap enough given the alternatives, and it doesn't really give customers the main benefit of ec2 (compared to existing alternatives)
So the answer is yes you will be able to replicate a traditional EY cluster setup on AWS in a few months.
To me this looks like Heroku but with more flexibility.