At the time, Ines Vargas, Microsoft's director of support policy, said the decision had been made in part because the company recognized that consumers were keeping their computers for longer lengths of time.

On Tuesday, Microsoft explained its reason for extending XP while keeping Vista at five years. "Microsoft's decision to provide an extended support phase for Windows XP Home and Windows XP Media Center was limited to those specific versions of the OS," the spokesperson said. "Given that Windows Vista recently became available to consumers, it is premature to make any decisions about an extension of consumer support at this time."

Michael Cherry, an analyst at Directions on Microsoft, said he knows why Microsoft is, at least for now, holding the Vista line at five years. "Because they're optimists, they think they will have Vista's replacement out in time to beat that deadline," Cherry said.

Likewise, the decision to extend XP support was taken for more reasons than keeping customers happy, Cherry added. "Microsoft was so late in getting Vista out, that there was a danger of XP falling off support within a very short time."

Microsoft posts its support schedule for the various versions of Windows .