Ok, but most consumers have no stomach to go mucking around with OS components. The modularity of OSs is at too technical a level. And most third-party apps are trying to solve slightly different issues, with lots of overlap in functionality. There are no well-defined, standardized extensibility points are needed<p>In any case, if I were to write an app for any OS, I still have to think about authentication, UI, storage, etc. There is no tight environment where I can just submit a more performant file sorting algorithm, for example, and be paid by users who choose to use that in the OS. That is the idea.