When Windows 7 is available, it won't be the first time Microsoft will have two OSes on the same code base in the business market at the same time. Windows 2000 Pro and Windows XP Pro were built on the same code base as well, and many business customers on Windows 98 waited for XP instead of moving to 2000, Gillen noted.

Windows 7 is essentially the second release of Vista, an incremental update that will include some usability features but not "cause a rift for Windows Vista applications" during a migration, he said.

It will essentially be about as painful for customers to move from XP to Vista as it will be to move from XP to Windows 7, Gillen said, corroborating Schuster's warning. He agreed, too, that a migration from Vista to Windows 7 will be far easier.

However, Gillen said that Microsoft's argument that customers should pick one or the other is more in its own self-interest than an actual necessity for enterprise customers.

"[Microsoft] is trying to use every lever they have to try to encourage customers to move," he said. "But customers are going to make their own decisions based on [their own needs]." Some customers may find they can stay on XP indefinitely as long as they can continue to patch and support their applications on it. Microsoft ends extended support for XP in April 2014.