Windows XP isn't eligible for a free update to Windows 10. That is more of a concern for home- rather than business users of Windows, but if you are running a Windows XP shop and looking to upgrade, there will be a cost attached. Of course, there is a cost attached to not moving on from XP. Potentially in terms of the security threat, but definitely when you take into consideration lack of support for third-party software and peripherals.

Something else to keep in mind is usually older computers have XP..and those computers may not even be able to run Windows 10, anyways..