windows 7 and drive space usage

ok i know that windows 7 is supposed to be great and all, but why is it that the windows folder is a lot larger than that on vista. wouldnt that still downgrade performance? and whatever happened to the "ability to run on low end machines" some people (not saying me) dont have a hard drive higher than 20 gbs. in my opinion, this is just ridiculous. we are talking like 3-5 gigs more than the windows folder on vista