Isn't that why Heroku and other PAAS do custom pricing for their larger customers?
That's one possible solution, with a major challenge being that Amazon regularly cuts AWS prices (51 times as of January). Competing with Amazon is rarely a winning strategy, although Salesforce has similarly razor thin margins despite having been publicly traded for more than a decade.
That reminds me of this challenge Heroku is currently facing (http://go.theinformation.com/884b08):
> When an app hits a certain scale, the cost of Heroku can be many times that the cost of cutting out the middlemen and running on AWS directly.
> For that reason, Heroku finds it tough to attract big companies. They know they’re going to operate at a large scale, and they’re open to taking the trouble to cut out the middleman of a Heroku if the savings are great enough.