Patents are opt in while copyright is opt out. If APIs are copyrightable Google will never get access to the Java API, ever. If someone gets a patent then it will expire eventually. Of course Google wants to go back to the status quo: APIs not being protected by IP rights.
Is this actually the status quo? There are patents on APIs around, and since they were granted, it would seem that USPO, at least, doesn't think that APIs are inherently unpatentable.