It's not exactly so, if you use a server that spawns child processes: http://michaelvanrooijen.com/articles/2011/06/01-more-concur... you can potentially handle 3-4 requests per dyno at a time. That doesn't fix the root problem, though.
EDIT: will need to look into our memory perf though, looks like we'll need to do some work to get more than a couple of workers.