My understanding of XP suggests you're right. However, no methodology is 100% right in every situation.

I think that doing a great deal of work to generalize something when there's no need is obviously silly. There's no reason though to do something in a less general way which doesn't run any faster and requires just as much work to implement. I'm talking about looking at the problem as a more general case, not about working a more general case into the code as an afterthought.