The whole XP (eXtreme Programming) movement came out of the Consulting domain. "jasim" in this thread explains the context where it makes sense. The company i had worked for had jumped on the XP bandwagon when it came out (we even had Kent Beck, originator of XP himself come out and do presentations!) but i never saw anything unique about it. It was merely a systematic way of working much more closely with the Client and doing rapid implementation iterations towards the known requirements which all experienced Engineers/Managers/Companies were already doing. Except it wasn't a dogma with them but adaptation of a sane process to a context. I always thought of XP and its successors as marketing by successful Consultants rather than any true insight.

You might want to take a look at the original short book "Extreme Programming Explained" by Kent Beck and form your own opinions.