System 76. Just Google it. They bare built specifically for Ubuntu and are within your price range. Their laptops are actually Clevo/Sager remade to work perfectly with Ubuntu.
One thing though, I do not agree with you that game devs target consoles first, before porting to PC. In fact, I its the other way around. Battlefield 3 and the engine it is built on, targeted primarily PC performance, scaled down to run on consoles. Same thing for most games out there.
Gabe announced that windows fails and he wants to go linux. So based of this, the console will be Linux based that either allows to run Windows based games, or, what I think Gabe is aiming at, urging the developers to make hardcore games for Linux. Either way, this will be the first time Valve is going into hardware (at least to my knowledge) so we'll see where this goes.......
All in all this is about integration and innovation :)