I dont understand those people. Just buy a monitor at that resolution if you're going to run the lower resolution.
OT: Take a FPS gamer and a console gamer, put them in the same game. And the PC gamer will eat the console gamer for breakfast.
What about people playing other generes professionally, like fighting games?

I told you not to give me the PC gamer master race ******** and yet you did. Are Halo competitive players any less SERIOUS than competitive PC FPS gamers? Yes, they might get owned by a pro CS player with a mouse and keyboard in a hypothetical competition just because the mouse and keyboard input method is objectively better than joysticks, but that doesn't mean they are inherently less serious about their career.
They don't just "low" everything and be done with it. It certainly doesn't sustain 60 FPS.
Except they
often do just "low" everything and be done with it. Many of the streams on Twitch.tv are clearly
just "low." I haven't tested SC2 myself on low and 2880x1800 - I'll test it and report back with my findings, however - I have a feeling it will be pretty close, but I could be wrong

I know it runs with Ultra on a lower resolution just fine.
Sure there is. Monitors which support 1080p @ 120 Hz are simply too large (23 inch minimum). That's why the Pros choose 1680x1050. They come in 21.5" sizes which apparently has been shown to be optimal for gameplay. (Too lazy to find citation, Google it)
So now you're introducing refresh rate into the equation? Barely any laptops support 120 Hz anyway.

Why are you even looking at a MBP if you want 120 Hz gameplay? The monitor is 60 Hz. You even imply above that 60 frames per second is enough - unless your monitor is doing some kind of interpolation (which would be bad for gaming) or you need 3D (which is bad for SERIOUS GAMING, in your definition of the word), if you are running at 60 fps or over, you would not notice the difference between 60 Hz and 120 Hz. Besides, your whole "dur hur 15" Retina MBP is bad for SERIOUS GAMING" point is moot when you can just ****ing plug in an external monitor, which any SERIOUS GAMER would have on hand anyway…
Besides:
http://www.newegg.com/Product/Produ...peTabStoreType=&AdvancedSearch=1&srchInDesc=#
NO RESULTS for ANY 1680x1050 monitor at 120 Hz.
http://www.newegg.com/Product/Produ...SpeTabStoreType=&AdvancedSearch=1&srchInDesc=
60 results for the venerable 1080p monitors at 21.5" size. None with a 120 Hz refresh rate, granted, but there aren't any 1680x1050 monitors at 120 Hz either!
But if you ONLY had a choice between 1680x1050 on an rMBP and a 1680x1050 on a uMBP and you had the laptops at a side-by-side, you'd pick the uMBP. In some games with their own text rendering API that doesn't play well with downsampling, you would even call the rMBP unusable.
You've got "downsampling" and "upsampling" mixed up. The data has to be upsampled to the native resolution, not downsampled. Downsampling is what the rMBP does when it renders the larger "scaled" resolutions at 2x and have to scale them down to 2880x1800, a technique which isn't used in full screen games (or Windows for that matter) anyway
I challenge you to find ONE example of a game released in the past few years that is ruined and made unplayable because of blurry text by playing at a lower than native resolution. Game developers have to take this into account. Usually the scaling is done in the screen itself, so the use of an alternate text rendering API would NOT affect the readability.
I think you have no idea what you're talking about.