personally, i think there should be a setting (and i think there will be) so you can turn the visual enhancements down to a level of Windows XP or Windows 2000 so you dont need even a 64mb GPU. But 1ghz and 256mb Ram would sound right for Vista.
It's not about caring for the users Eric. MS optimises the code on every version of windows to reach their aclaimed "uber productivity" they brag about. I forget XP boots 15% faster and loads apps 10% faster than 2K or are the percents reversed? Vista is aiming even higher. They have already optimised the code and will only improve it over time.
it runs slow because its in beta. It should still be able to run just say on a 1ghz Machine but all the visual settings should be able to be turned down or off.
ps vista will have a thing that detects what your computer's capabilities are and optimizes itself for that setup ie if you don't have a good enough graphics card to run the aero graphics it will be turned off audomatically.