Back in 2001 I was working in IT in a healthcare environment that spanned 3 physical buildings and approximately 7000 desktop systems, I was working IMAC, installs, moves, adds, changes. The hospitals were upgrading from Windows 98 to Windows 2000. All the systems arrived to us new in the box from the leasing vendor with copies of XP Pro. We opened the boxes, pitched the copies of XP into the trash and installed the hospitals templated version of 2000.
I imagine a whole lot of that goes on still today. It was critical that all systems there be stable and due to legacy software interacting with a wide variety of crucial devices we could never have the newest OS installed until all bugs were worked out in service packs. We were typically always an OS behind the current release.
So today, they are probably running XP and in no hurry to upgrade so all new systems coming through the door for deployment -- the Windows 7 OS gets pitched out the door.