Recently I was involved with a medium sized desktop roll out for an insurance company in Australia, they decided to stick with Windows XP & Office 2003 because this combination does everything required, is stable, secure and the users & admins are comfortable with it. They expect to be with this combination for at least 3 years.
Obviously cost savings were a factor, an OS upgrade 7 would lead to an update of office, which would require a new set of standard templates/documents, costly staff training and not to mention the server side of things. Office 2010 conveniently doesn't support Exchange 2003. When considering 5,000+ workstations these things matter.
Microsoft is failing to demonstrate the real benefits of an upgrade to Windows 7? Looking at http://windows.microsoft.com/en-US/windows7/products/features, the main appealing item is 64-bit support, but it's possible to run XP 64-bit. Two features that interest me are the Windows Deployment Tools and the new Windows Search services.
It is not best to swap horses while crossing the river. -- Abraham Lincoln