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.
Once it hits the fan, the only rational choice is to sweep it up, package it, and sell it as fertilizer.