I don't think the 2wd is a likely explanation at all, actually. I think the much more likely explanation is the driving style, which also most don't have any experience with.
I doubt that. Even driving very conservatively I can only do 18-19mpg at best on the freeway with a well-tuned '03 100 cruising over a reasonably long distance. I really don't think it is possible to get significantly better than that in the OEM configuration, both from that first hand experience as well as from the vast majority of what I have read on MUD, cow magnets and hydrogen generators notwithstanding.