Good test, muki. I've never had the chance to do a check like that. But I do know that with the wi-fi routers at work (some Linksys and D-link routers) there's no dip in the battery indicator if I leave it on wi-fi for 12 hours (with the occasional email notification and things). A non-PSM router, on the other hand, will drain the battery in two or three hours under the same conditions.
Oh, and poor signal will also drain the battery much quicker.