That's where a bit of skepticism stems from, as I've dealt with both of these databases first hand, also various other stacks ranging from java, python, ruby, even lua.

The not-so-stellar uptime record of Heroku shows that making one size fit all is quite hard, even when you're doing it only for a relatively small set of components.

Doing it well for nearly all of them is nothing short of the holy grail in systems management.