So, you want to provide an API for the world to use?

Agreed. Most use case scenarios will involve a code library wrapper around the API. There's some unique challenges in building the library as well though - in a small & quick start-up, it might be hard to find experienced programmers in the 7-10 languages you'd want to support. When you get an experienced PHP developer to write the Java API, it will work, but will it "work"? In other words, will it follow the conventions that Java programmers are used to (classes, objects as parameters, static methods, etc.), or will it simply be ported PHP code to Java (hashtables as parameters to every method, fewer objects, etc.).

I've often said you can tell how good a code library is for an API based on how often the user needs to read the API documentation - ideally, they would never need to even read the API. After all, why have a code library if the users still need to look up the exact spelling and capitalization scheme of string parameters, or look up the numerical codes in return values?