And because Windows 7 machines tend to have at least two gigs of ram, a much larger hard drive, and a vastly superior dual-core processor, their functional value should last a little longer.
That marathon battery life is made possible in part by the slow-spinning 4, 200 rpm 30GB hard drive and low-power (in more ways than one) Core Solo U1300 processor, running at a sprightly 1.06GHz.