Many of these machines would have perished under the weight of Vista.
‘Falling Back in Love with Microsoft — and Windows 7’
http://www.pcworld.com/article/174266/falling_back_in_love_with_microsoft_and_windows_7.html
 Microsoft long ago admitted that they had to come up with something that would "live" in the "netbook" market. That was one of the key driving forces in the design.