Sun in fact did litigate over Java, as the article offhandedly mentions, though the motivation there was that MS different version was fragmenting the language, and undermining the compatibility of "write once, run anywhere".
I agree with the article that even a few billion in damages isn't worth it to Oracle. There must be some strategic advantage, quite possibly in some negotiations with Google that we haven't heard about (and perhaps will never hear about).
The point made about the mobile revolution is the right kind of path; another revolution in progress is the cloud. There is definite overlap between Google and Oracle in the cloud, with Google's technology expertise, and it being used by the enterprise - that's probably what Oracle hopes to gain.