But still, why is it relevant or meaningful to compare the market share of Bing.com vs Yahoo.com since the two are now in a formal partnership going forward? Isn't the central issue: Bing + Yahoo vs Google?
Also, Microsoft doesn't really want people searching through Yahoo.com, in a few years time they could power their results through Google and Microsoft wouldn't be better off. They want brand recognition for Bing, so gaining market share for Bing itself is better for them.