Good question. No they are not all one-time purchases (that would make life too easy!). Take a look at the image I've attached with 5 examples of the different types of license combination developers can offer.
The Lab - Free consumer license - Free commercial license
Serious Sam 3 VR BFE - Paid consumer license - Paid monthly commercial license with discounts for multiple copies
Job Simulator - Paid consumer license - Paid monthly commercial license
Tilt Brush - Paid consumer license - Paid lifetime commercial license
Flappy Flappy VR - Paid consumer license - Paid lifetime commercial license - Paid monthly commercial license
Note that every license sold on Steam both consumer and commercial are per station, or as Steam calls it for the Steam Cafe program, "for one seat". The games which are monthly specify it as such at the top of the license agreement, Job Simulator for example is "$87.99 at the checkout, and auto-renewed every 1 month(s) at $87.99 per license."
So VERY expensive if you're running an arcade with a lot of stations and want it on all of them. I don't know why anyone would bother and can't imagine they sell many commercial licenses at that rate. Most of the time only the lifetime ones are worth the investment and I'm so glad I got Job Simulator before they switched from lifetime to back to monthly at triple the price (yes devs can do that, and it sucks, but it doesn't invalidate the lifetime licenses you've already purchased).