I doubt it was that serious, but you never know: the Department of Justice had announced that they were looking into the connections between the two boards, with both former Apple boardmember and Google CEO Eric Schimidt being one link, and Levinson being the other. Not that the DoJ was really breathing down any necks (they'd only requested documents, and there were no signs at all, other than, you know, Google Maps being an original iPhone application, that there was any collusion between the two companies).
But it is possible that between them, they decided to play it safe, and with the two companies getting closer and closer to competition every day (with Google's Android OS and the continuing saga of Chrome going on), this is probably for the better. Levinson and Schmidt, meanwhile, will both still continue to make millions of dollars anyway. So they have that going for them. Which is nice.