Google’s I/O developer conference this week gave each of its mobile operating systems a day in the sun, setting out ambitious roadmaps for both, which nonetheless went a long way to end the confusion about their respective roles. More broadly, Google was setting out its stall against all its key challengers. The launch of its cloud music service and app store stepped up the fight against Apple and Amazon; Chrome OS promised the death of Windows and a new phase in the browser wars; and the pledge of a unified, ubiquitous Android laid down the gauntlet to iOS and to the WP7/Nokia/RIM axis. There are big question marks over all three of these key strategies, of course, and some competitors…