Thanks to Xbox and Xbox 360 I was able to play PC games like Doom 3, Morrowind, Half-Life 2, Left 4 Dead, and Oblivion. Yes, those games aren't exclusive -- and neither are Gears of War or BioShock or Mass Effect -- but I was able to play them all on Xbox and Xbox 360. So buying an Xbox is a pretty good choice for fans interested in those games and in true Microsoft exclusives.
Is an Xbox 360 alone sufficient for all your gaming needs? I don't think so. But it might be the right choice for some people, especially considering the costs involved in this hobby.
The important thing is this: just play the games wherever you can get them.