I've no problem with the US taking on the role of the world's policeman, but I think it may have had more of an impact if its concerns were more than those surrounding oil. For example, where were they when China invaded Nepal? And where are they now as they're still there!
Afghanistan may not be oil rich but it's a good place to lay an oil pipeline across. And that's exactly what the US are going to do now that the Taliban aren't there to stop them.
If it isn't about oil, why do the Americans themselves talk about it so much? I haven't heard mention of the Persian rug industry being "held in trust for the Iraqui people". As for Blair, he is trying to re-build the "special relationship" that Britain allegedly (I use this word as I never saw a whole lot of U.S. investment in the U.K.) had with America,
and he is prepared to risk sevice people's lives to be seen as a World Statesman.