Today, APIs are the API. There are APIs for Amazon, Bing, Facebook, Flickr, Google, Netflix, Tripit, Twitter, and most of the other major web services you use. Given that bits and pieces of your personal cloud are stored in various services, a developer may want to create an app that interacts with more than one of them on your behalf. To do that, they must learn how to use each relevant API. Nowadays they tend to share a common set of conventions, but each API is its own protocol. So while there’s a lot less data friction than there used to be, there’s still a lot more than there needs to be.