Ian Sane: Exclusive Content isn't even 100% true.
Halo wasn't a unique game. You weren't missing out if you decided not to buy an Xbox to play Halo, yet Halo single handedly sold the Xbox to the American public.
However, Nintendo's Gamecube had atleast two very unique games right after launch. Super Smash Brothers Melee, and Pikmin. Yes, SSB was available for N64, but not nearly as polished or as great an experience. Then you have Pikmin which deceptively looked like an RTS, but it felt different. And if I must say, Luigi's Mansion was also an exclusive content game as well, that provided a unique puzzle type gameplay...sure it wasn't recieved well but it was exclusive.
Gamecube even had Super Monkey Ball a 3rd party exclusive game, that was a blast.
In fact, I would argue that if you look at Nintendo's library for unique exclusive content it is much better than Xbox and I think very similar to PS2. Yet it is somehow 3rd.
The point I am getting at is: Its less games, less exclusive content, and sadly more about perception and "coolness." The thing is that Coolness will get you in the door, but the games is what will keep you, and you better have good games.