It doesn't really matter all that much which distribution you are running (it matters a bit cpu wise); Linux' drivers are not power optimized in the degree they have been on Windows (or OS X for that matter). Actually,one of the main focus points for Windows Vista/7 was power optimization and they really succeded in that matter (of course the manufacturer produced drivers needed to be updated as well, so sometimes you actually used more power after upgrading).
The money in Linux has always been in BIG IRON (as in server platform), and the drivers have thus mainly focused on performance. Power efficiency is mainly a thing of concern to end-users and it simply does not pay (for hw producers) to put a lot of money into this market.
For comparison I could get a maximum of 1h50m when running Ubuntu 8.04 on Acer Travelmate 6292 (screen dimmed way down), whereas I could just squeeze out close to four hours on Windows Vista. That was with power optimized drivers and power management software from Acer. If just using the built in software from Windows I lost close to an hour of battery time.
This really is not a new thing and it has not improved in a big way in the last few years either. Some google searches can bring you up to speed on the matter.