I also have noticed huge differences in battery life depending on wifi connection. At work, I have a rather fresh Netgear 802.11g router, which also happens to sit right on my desk. I can have my N800 on all day with quite a bit of usage, and the battery won't go down more than a tiny bit. At home, I have an ancient 802.11b access point (I think it's also a Netgear) with the signal passing through a lot of walls, and I can't seem to get more than 2 or 3 hours of battery life. I've resorted to going to offline mode whenever I don't use my N800, but as soon as I'm online, battery estimate goes down to 2 hours in regular surfing mode.

Until now I blamed it on the distance from the tablet to the access point (and the amount of bricks and concrete between the two). But it seems quite plausible that it might have to do with the protocol, too. Maybe 802.11b has less efficient power saving features than later protocol variants?