According to this article the battery drain when running Vista on a laptop is because of the Aero effect. I guess most laptop makers will put out some kind of power management scheme that will give you a better balance between battery life and performance.

“When Aero is turned off, battery life is equal to or better than Windows XP systems. But with it turned on, battery life suffers compared with Windows XP”

Vista draining laptop batteries, patience [ZDNet.com]
via [Gizmodo]