But that's the thing: places which fit those requirements usually run some IBM solution (AS/400 and the likes). I've never encountered VMS in production before, so I'm really curious to some concrete examples of companies using it.
In contrast to some of the other comments here, we weren't using it because moving to another OS - or architecture - would have been a pain. In fact, our software originally ran on x86 machines at some point in the distant past, before we migrated it to OpenVMS relatively recently.
I don't know why OpenVMS was given preference over GNU/Linux, *BSD, or Windows; I'm guessing that the technical managers above me had their reasons, but I couldn't say what they were.
I left that job a few years ago, but I think that they did intend to eventually phase out the VMS systems as our new, GUI-based product slowly replaced the older text-based one.
We have almost entirely moved away from it and onto Linux but considering the decades of code and systems built on and around it, it is truly a monumental task to move off VMS while keeping a system used by very high paying clients running smoothly.