"So what is it a case of, China/North Korea not having oil, or would it be their massive firepower ?"

It's both of those, Richie. Politics is a matter of sheer pragmatism, and pragmatism trumps principle. Regardless of their rhetoric (which is mostly designed to placate their own public and make themselves look noble), governments undertake military actions of choice only when they think they can:

1. afford to do it
2. and succeed at doing it

Sometimes they miscalculate on both of those accounts. Time will tell whether they have miscalculated when it comes to getting involved in the conflict in Lybia.