The us uses hsdpa and 3g. So i'd be willing to bet they won't be added for the uk.
I'd take that bet!

HSDPA/UMTS is only available in around 10 cities in the US at present. Cingular has a bit of coverage and T-Mobile has absolutely zero.
I'm willing to bet that they didn't have the HSDPA/UMTS component ready for the initial launch. In the US, that doesn't matter much as HSDPA/UMTS is available to many customers anyway. By the time the iPhone is released in Europe (9 months+ from now), I'm sure they will have everything sorted out. European operators have spent a lot of money on their 3G networks and I'm sure that they will not sell such an expensive 2.5G device.