Not anymore... X-Box owners are software whores. Even when their is a period of no good games third party crap and shovelware is selling. This REALLY appeals to developers... Look at your cloettion of GCN games. How many do you, which are not first or second party games??
It's not like Nintendo couldn't buy a few exclusives and make even more profit on them in the long run.
Nintendo is a victim of their own success.