Sony stopped doing it, look at where they are now. They get alkot of multipatform games out of default just for having HD.
MS has all the $$$$ in the world and assumes that they can continue to buy their way to the top. They have yet to turn an actual profit from the money spent on the original Xbox, so you do the math on that.
Nintendo is (too little too late) trying to reach out to 3rd parties by offering marketing support, but what they probably should do is send out a few bodies and give some development & marketing support in exchange for exclusivity(also Nintendo would get a larger share of the profits too).