My understanding is that there's a few things at play in this. The first is the screen makers which you mention their reasons for doing it. The second is one

My understanding is that there's a few things at play in this. The first is the screen makers which you mention their reasons for doing it. The second is one of bandwidth to the display, my understanding is that that is the limiting factor here. At 2560x1600 you've got (2560 * 1600 pixels) * 24 bpp * (60 frames/second) about 5.5 Gigabits per second. at 3840x2400 (1.5x of above) you've got 12 Gigabits/s. At the moment HDMI has a bandwidth limit of 8.16 Gigabits/s after overhead, which isn't quite enough to do it. Display port 1.0/1.1 also had a limit of around 8.6 Gigabit/s. Displayport 1.2 however goes up to 17.28 Gb/s so it should allow for the larger displays but I've not seen many non-apple display port monitors myself. DP 1.2 came out in December of 2009 according to wikipedia so it should have started to filter out to people by now but I've not looked into that.