First, Google did a lot more than copy the APIs (ie. reimplement the class libraries from scratch against the published interfaces). In many cases they directly included decompiled versions of the original class files.
Secondly, as to whether APIs are or should be copyrightable, consider an analogy in literature. If the source code is the novel itself then the APIs are the character names, chapter titles, and plot synopsis. Clearly a lot of creative and original thought processes go into designing a good API and so ought to be protected by copyright. The real question, to which there's no simple answer, is whether writing something compliant with those APIs ought to be exempt as "fair use".
Biting the hand that feeds IT
