Because it describes what a stack overflow is, rather than being a site named after the thing?
That would be my thinking. Ok so maybe wikipedia doesn't have to be the top result, but I'd rather have results relating to the thing I'm searching for come above sites just named after it.
Oh maybe, and maybe they search for that more often than they search for the thing it's named after, and maybe more people would find it more useful that way.
I am willing to bet the City of London against a house-brick that the vast majority of people searching for 'ford' are not looking for a definition of the river crossing, but rather the motor vehicle company named after the man named after several other generations of men named after such a river crossing.
