They are mostly on subscription; but what is the rationale for subscription? The right to upgrade, and the ability to have all machines running the same version. Remember, that in order for subscription license to be valid, it is usable only for machine that came with OEM license in the first place.

I once worked for a corp that didn't have subscription. The rationale was, that is was not important who was running which version at their computer, and the subscription was thus a cost on top of OEM license that didn't bring any value. Since the computers were refreshed every 4-5 years anyway, they always had a supported Windows version.