I think that Yahoo prefers shorter pages and Google longer ones but I could be wrong. Yahoo might also, as cooliojones suggested, have a lousy algorithm; I think generally Yahoo is far behind in coding and they don't seem to care much about their users' experiences (their e-mail system is slow and way too ad-laden, for example, even compared to pre-Google-Mail competitors). If it wasn't for inertia, -- if everyone had to start over from scratch one day -- Yahoo wouldn't survive. That's sad because I do remember the days before they got so greedy, when it was just a guy publishing his bookmarks, and it was not a bad site; I used to use Yahoo all the time as a directory, the same way I'd use the Open Directory if it wasn't so darned slow, before they started charging $300/year to "consider" your links.
Man Yahoo is so weird sometimes, plus I only seem to get traffic from Google anyway, even though msn and yahoo are so big, plus im indexed in them. Who knows.
I have just the opposite problem. My site has ranked #1 for log furniture in Yahoo, but I can't even get on the first page on Google. Go figure!