Ok fair enough, but you have forgotten a few things that come std with a notebook. For instance on my ENVY i have a full HD display and a blu-ray drive which would sort of push your budget up a bit. Now there is no argument that you can gett better performance from a desktop rig. The point i'm trying to make is that there a well priced notebooks out there that would blow most "gaming rigs" out of the water.
Based on a study (done by sn3rd) i followed closely last year it is not the brute force of the graphics card but rather the package as a whole. Specifically, we noticed that a asus gaming notebook out performed a number of desktop pc's with at least the same specifications or better.
Not a chance. I'm sitting with one of the reasonably priced notebooks right here, as well as a crappy gaming rig with a nice GPU(C2Q Q8300, 4GB Ram, GTX570) and trust me there is no comparison in games. For 3D rendering the Laptop is roughly 1.65x Faster but in games due to not having a proper GPU, it gets ugly if you compare them.