If you get a "real" gaming laptop you can chose between being able to cook your lunch on them, enjoy your fans making an effort in trying to mimic a launching jetfighter, or you get both. None of that is very appealing to me.
On top of that, a laptop is less forgiving when you need to replace hardware, they tend to be more expensive and what's the point really? Playing games from your couch? What games do you play on a laptop where you can properly use a mouse and keyboard while you slouch about?
So if you don't play while sitting on the couch, you don't really need a laptop. And unless you're constantly traveling all the damn time, you will hardly make use of the mobile aspect.
In any case, you can put all the hardware in the world in a mobile device, but none of that will change how it's utilized. What do you play in your coffee-break or while you're waiting for the bus? Do you slap out your ultrabook and fire up your current mmo, or do you play a flashgame to waste a couple of minutes?
A videogame is something you play in your sparetime, in most cases you're at home because you're not working or whatever. And if you're at home, you don't need a mobile solution.
I mean, i honestly don't care if you feel like you really need it, it's your money and your decision. But i'm highly sceptical about ultrabooks/laptops replacing the desktop anytime soon.