The following URL is the KB article, which describes update that triggers the invitation to reserve Windows 10, mentioning that Enterprise machines do not apply:
HOW TO UPGRADE TO WINDOWS 10 NOW:
There’s a ton of great reasons for a company to deploy Windows 10, including
Universal Apps that enable you to extend your code base and/or future code effort across the entire Windows spectrum
A host of attractive, industrial-strength BYOD options for more than just tablets and smartphones
The most efficient and consistent use of latest generation hardware including touchscreen and security measures
As a developer, I’m very happy to promote the platform I most want to work on… I really feel that Windows 10’s success is the foundation of a lot of others’ success, including my own.