Yep, as simple as possible, no simpler. (NoSQL is another example)
I think a central source, like a database, needs to cater for every possible use in general (which the relational model does); but if you're doing something very specific, it's crazy wasteful to do it with full generality.
I am curious if someone can work out how to make a simple API that is also fully general (I think it has to be equivalent to the relational model - but it's early days yet).