Why do PaaS services like Heroku exist that simply re-sell Amazon AWS?

Why are services like Heroku so popular when all they really do is set up AWS servers (which is fairly easy) and significantly markup the price? You could easily setup the servers yourself and pay less than 25% of the premium that Heroku charges.

They make it slightly easier. And a much better experience. Trying to read Amazon docs or navigate their web site is a nightmare compared to Heroku. Heroku is very Zen. Amazon is confusing and schizophrenic. Things in Heroku just seem to work. Their documentation is very succinct, complete, and accurate. They have a nice support team (though even they don't always know the answer), but for Amazon, you have to pay extra to talk to a person.

IBM's motto was : Sell them yesterday's technology with really great service.