Well, netbooks are meant to be cheap more than portable. They're small as a side effect. And, batteries are an expensive part of the laptop - probably the single most expensive part, or if not, behind the LCD. (Hence the tiny useless batteries on most netbooks.)
That's also why I'd automatically get the extended battery if I get a Fujitsu P1630 - then it'd get about 5 hour battery life, and still weigh 2.5 pounds. And it doesn't have the CPU tradeoffs - 1.4GHz Core 2 Duo, my current machine has a 1.6 C2D. (It has some storage tradeoffs, by virtue of having a 1.8" drive, but...)