Old OS
While going to Win 8 full timex is unlikely for me [I've tried it and don't like it], Windows 7 is a vast improvement over Vista [which I won't get into] and Windows XP.
First, with Windows XP, many computers running them are at least6 years old [when Vista first came out] and some are breaking down or just dying a slow death. So if a company is using Windows XP and a system dies, what are they doing? Buying a system with Windows 7 or 8 on it, scrapping the OS and putting Windows XP on.
No way of knowing but I'm sure most Win XP systems are strong enough to run Windows 7.
Now Windows XP is an old OS. You need drivers to install the latest hardware. Wireless was problematic [which is why manufacturers included their own wireless utilities]. USB3 support wasn't built in. Neither are other recent technologies.
Deploying Windows 7 [while bulkier] is easier than than Windows XP.
If in a workgroup, Homegroup feature kills that problem of accessing resources from another computer. No need for passwords, duplicate accounts, etc.
Group policies for domains add much more options to locking down systems.
I can go on and on.
Now as for why CIOs aren't pushing? They are a bunch of idiots. They have had years to prepare for the change but it seems like few bothered to look ahead [I know of an ex-boss who was like that]. Then they will rush to migrate which will probably cause problems and mistakes.