Noway

Yahoo Launches Ad Campaign to Lure Searchers From Google

I concur with G and monkeyman. Search shares today is not about relevancy of the engine, but its about the distribution.
Monkeyman mentioned FF browser. Another huge increase is Google's deals with pc makers like Dell, which installs Google crap on new PC's and they're a little tricky to remove if you're not pc savvy.

Its similar to how MSN/IM/hotmail/IE is so popular around the world. they come default with the OS and 99% of the people don't bother to change them.