There are some changes between Yahoo and Google. One explanation I came up with was that google seams to rank sites on the number of quality links coming in, while Yahoo ranked more on the number of links and not so much the quality. I would say build more inlinks to you site and you may start to rank better in yahoo.
With Yahoo having about 1.4-to-2.5 billion searches per month it is worth the effort to get ranked. I seem to hold close to the same positions on Yahoo and Google for various keywords. The funny thing is it is often for different pages. Actually, Yahoo comes closer to returning the correct page than Google does. An example might be for "used pc games" Found on the second page of both Yahoo and Google. (soon to be page 1... I hope) Google points to my main page and Yahoo points to the PC category page as it should. For my other terms that Rank on page 1 of Yahoo I get enough traffic to pay for my overhead. Guess that makes Google traffic all profit
I have a similar problem. My blogs get indexed by google within a couple of hours after submitting a sitemap. But with yahoo, it failed miserably. I would think it's okay but it would be even greater if my sites get indexed by these two search engine titans. It would mean more traffic and, obviously, more money.
In my experience, it's not the number of inlinks in yahoo that makes the difference. Yahoo search is based on inktomi which Yahoo purchased to replace the google results that used to power the yahoo search. (1) Inktomi was more about on page seo. So that's one angle I'm looking at. (2) You raised the sunject of links. Rather than the number of links and the quality, perhaps the kind of links makes the difference. I put up a new blog a few months ago. I've noticed that it has started to rank in yahoo for my targeted keywords after doing directory submissions.
Google likes fresh content more than yahoo. Blogs get indexed a lot faster in Google especially if you burn your feed with feedburner.