Dan Nexon, I think, closes the argument that I'd had with Quiggin a few weeks back:
Consider that the United States is currently engaged in two major military operations and yet it has significant forces converging on the Libyan coast and on Japan. Puts John Quiggin's insistence that the US is now one of a number of major powers into perspective, but not necessary in a way that speaks well of current US budget priorities.
Aside from the that I'm not quite sure what the last clause means, this is exactly right. The US, half a world away from both Libya and Japan, is both closer and more able to intervene in both places than the other significant powers in Western/Southern Europe or Asia are to intervene in either. And is able to intervene in variable ways.