I think the reason Dell doesn't put such screens on it's laptops is cause software ain't there yet. I have a retina macbook pro and I have tons of problems with a high dpi screen in windows if I don't want to run it at full resolution (I mean 2880x1800 on a 15 inch is basically unreadable). If you use windows's scale feature in Windows 7 in some programs you get only the menus enlarged and some other stuff at acutall resolution. If you just change the resolution to let's say 1920x1200 all of your text looks blurry and annoying (the 150% increase in display scaling also has the same effect).
ok.. but windows 8 has high dpi support. yeap it has it.. just that the apps didn't catch up to use it yet. not even talking about problems of porting some apps that work wonderfully on windows 7 but fail to start in windows 8.
I think it should be more of a push for Microsoft to start properly supporting HiDpi screens.