It'd be a pain at first, but look at other APIs like a database ORM that supports MySQL, Oracle, MS SQL. The commands to the end-developer are all the same for any of the platforms, but the underlying API can use any of the supported database engines.

If the Ubuntu API were done right, it could be ported, to say, Fedora, and use any underlying fedora libraries without the end-developer having to change her code at all! It could be extremely useful. You'd have a Linux API that can source the best API to use for the end-users current configuration.