The copyright for that file dates back to 1991, back when Wordstar was still relevant. Like BRIEF and WordPerfect they have gone the way of the dodo.
I still remember having to use WordPerfect back in the day; but without the little cardboard printout you stuck to the keyboard's F-row it was almost impossible to use.
Are they still in there, I wonder? I doubt many people use them today, but it's not hard to imagine them tucked away in a menu somewhere, a forgotten island of once-important code...
BRIEF macros were the original scripting language for DOS.
The reality is, of course, that WordStar doesn't do anything special that there's not a modern replacement for. With the wide variety of software out there available to write documents, I'm sure that there's something that would word as well or better.
But the thing is, GRRM isn't interested in finding a replacement. He knows what works for him. And that's fine.
It's not about the tool, it's about the author.
Edit: "To all of you worried about my backing up my fiction. I write on a DOS machine that is physically separate from my Windows machine and has no connection to the internet. It cannot get a virus. Assuming someone was writing viruses for WordStar 4.0, which I think unlikely. It also has a built in mirrored drive, so everything I write is automatically copied to two hard drives. I back up frequently to floppy disks, less frequently to CD/ROM, every blue moon to a Zip drive. So I think I am pretty well backed up. The one vulnerability I have is that all these backups share the same physical location, so if my house burned down, I'd be screwed. I have looked into offsite backup systems, yes, but unfortunately none of them will work with DOS/ WordStar. (And no, don't ask, I'm not going to send any of you a disk for "safekeeping," I'm on to that trick)."
That's a sub optimal solution but it's better tuan what he's got now.