A Brief History of Windows (with apologies to Stephen Hawking)
Yes, it actually IS Windows NT 7.0
The reason some people get confused about the numbers is there are two distinct product lines prior to Windows XP and after Windows 3.11
Consumer OS Line: 95, 98, 98SE and Me
Professional Line: 3.5, 3.51, 4.0, 2000 (5.0)
Originally a merge of the product lines was intended with both a Professional and Home version of Windows 2000 (code name Neptune) but several issues prevented this and Me was released as the last of the 9x line to fill the gap.
Windows XP (5.1) represented a merger in the product lines and was a direct successor to the 2000 code base.
Windows Vista (6.0) was the first major kernel upgrade since Windows 2000
That leads us to Windows 7, although some would argue that it should have been a point release of 6.1 as in many ways the operating system appears to be a slimmed down and optimized version of Windows Vista.
For marketing purposes, calling it Windows 7 is far better than trying for Windows Vista SE. After all, most people were pleased with Windows 98
Biting the hand that feeds IT
