Well, I haven't used Vista so I can't draw a full comparison. From what I read, there are some interface changes. I suspect, though, that they pushed Windows 7 forward and reduced the number of changes just because Vista was a complete and utter flop. Even though most of the issues with Vista have been ironed out (eg drivers, programs not working properly), people still don't want to touch it. So they need to give the impression of a fresh start to get people excited. And it appears to be working...
