I think it's mostly because the dedicated servers at your host don't hide between the convenient API of a PaaS like Heroku. Much more things are happening when

I think it's mostly because the dedicated servers at your host don't hide between the convenient API of a PaaS like Heroku. Much more things are happening when you do git push heroku than when just pushing on a remote of yours. If you tried to write a few scripts to automatically deploy your code on N instances, manage http load balancing and all the nice but invisible features of Heroku, I'm sure you would be down more often than they are ;-)