they took the vista kernel, tore it down, and literally rebuilt it. they just didnt take a car and strip it down to bare essentials. they took the engine and build a new frame and everything around it. kinda.
First of all, the way it manages processes is WAY different than in vista. in vista it loads them one at a time where as 7 lodas them all at once durring startup making it a whole bunch faster.
i could go on and on about it, but frankly, i wont. it works better than vista, and i seem to like it more than my xpsp3 build.