>The fact that Windows XP has been around so long is really an accident. If it was up to Microsoft we'd all upgrade our machines every 3 years or so (consider Windows 95 – 98 – ME – XP – …). The problem with that was that Vista was delayed by a few years and – once it was there – it was so abysmally bad that when asked to upgrade, many people flipped MS the bird.
Microsoft's fondest wish is that everyone pays them money every year for nothing. The fact that MS wants a 3-year cycle and that XP's long life is a mistake don't matter, what matters is that, for the majority of people, there have been *two* operating systems: Windows 98 and Windows XP.
The first one most people used for 3-5 years, the latter one for 5-10 years. This is what people want, a *minimum* of 3 years of stability and 10 years is better. Nothing which breaks every 12 (or 6!) months will work.