Well, I have a MacBook Pro (Santa Rosa 2.4) and I got vista running on my computer via BootCamp. I think it actually runs Vista better on the MBP than on some other PC laptops.
As for 'why so many flavors' I really have no idea. I like Mac OSX because there's only one version that has everything.
http://www.apple.com/getamac/ads/
View the "Choose a Vista". It's pretty funny.