There's a difference between an embedded application like a grocery store scanner, and a general purpose computing environment. Heck, my brother (who works in SCADA) still has some *DOS* systems out in the field. Well, almost. DOS of course won't run on modern hardware, so when hardware fails, they run their DOS SCADA application that has been happily burbling info about voltages and pressures for decades in a virtual machine on said modern hardware.
But I doubt anybody is going to deploy a DOS system as a general-purpose computing environment. People currently running XP for non-embedded applications need to be planning their migration to Windows 7 or above right now, because once security fixes stop, all your XP systems that are hooked to the Internet will start spewing penis and breast augmentation spam non-stop 24/7 as well as be jumping-off points for hackers to explore the internals of your network. Maybe you figure retraining your employees to run Windows 7 would be more expensive than being a spambot farm and having all your corporate secrets shared with the Internet, but I suspect most people don't feel that way