People do not upgrade "just because". Well, sure, a small percentage do (you know, people who just have to get the latest and shiniest... YOU know what I mean, right?).
For the majority, either they upgrade "by accident" - when buying a new PC that, accidentally, comes with a new OS.
For businesses, it is not an accident, they evaluate that the OS 1) runs all the soft they use and 2) complies with hardware they use, and 3) is sustainable (security patches, support etc).
Because of that, businesses WILL have to upgrade, together with us, once XP support stops (hey, 2014 is NOT a long way out!), they buy new hardware (oops, sales printers don't have XP drivers anymore, or can't sync with the latest BlackBerry thingies!!!). Last, but not least, they upgrade MSOffice, servers and then, surprise, to use the new features they need components that are Vista-only.
Moving away? Macs or Linux, *IF they comply to the same requirements: newest hardware, stable support and problem-solving, and of course playing nice with the latest corporate drones gadgets!