Well for anyone who really knows the cycle of Microsoft and their release timeline for OS you would know that 3 years is about normal. Even for working OS's.
Windows 95
Windows 98 (3 years)
Windows ME (2 years)
Windows 2000 (Same year as ME)
Windows XP (1 year after ME, 3 years after 98)
Windows Vista (6 years)
Windows 7 (3 years)
So before anyone jumps and says that they have abandoned Vista is wrong. Microsoft has a history of releasing a new OS every 3 years or so. It wasnt until XP that they broke the cycle.