There are other spot color systems such as Toyo, and Focoltone. But at least in the U.S. Pantone is the most common system.
This isn't right. Printing presses don't come with inks, you mix inks and load them onto the press. Printers tend to only have CMYK, and that's also not true for many high end printers, because CMYK is a very restrictive gamut. Hell, the reason for the K is because CMY can't do a good black.
Nearly wrote "Maybe no license fees to map 271 year old color names in Adobe PSD files?" but thought that might be too obscure for HN. Apparently not. :-)
Good education below. To thread's point, in both cases (the watercolors, and Pantone), the work is in determining repeatable formulations, and building/maintaining a reference. It's inane, though, given the rest of ecosystem is licensed, to suddenly charge for the map in a PSD to keep working or go to black.
You can ignore Pantone entirely, put in whatever color you want, and nobody will know or complain. You can even use any color you want in Photoshop, then make a plate out of it for the press, and tell people the Pantone color you want that plate to be printed with.
But I sense a lot of the self-righteousness about the topic is coming from people who think that Pantone isn't doing anything, that RGB or CMYK can represent every color and Pantone is just selling them back to you. This is not true. Is Photoshop digging into users pockets again with another subscription plan? Yes.