At the same time, Japan is a stable liberal democracy, and normally they don't engage in sudden changes to long-standing relationships. That's why we prefer them; they're stable. Besides, the Democratic Party in Japan knows where the real threats in the region are, and where the friends are.
Seriously...which guy would you rather have at your back?
I am particularly heartened, though, by the idea that Japan and China can pursue better relations without it being seen as dangerous by anyone else. This is the kind of thinking that will help keep tensions low and relations productive in East Asia. China and Japan are the two main powers in the area, and improving relations between the two of them and with the US should be a no-brainer.