On some of the smaller lathes, sacrificing the compound for rigidity is often a thing, at least temporarily. You don't always need the compound, so a solid block in it's place works for some operations.
While I was also joking, it is also true. I play with the 7x mini-lathes and some of the folks who also play with them do in fact replace the compound with a solid block. I've also seen some model lathes that have all the goodies you'd want on a real lathe. Staying true to the Lego stock would make that a bit more difficult, though.
Currently trying to come up with a design for a motorized hbm. Here's all my machines.
That whole groups is cool! Personally, I'm working on having a full shop of real benchtop machines, but my kids outgrew Lego a long time ago, and when the Lego Technics stuff came in, I didn't have any excuse to get into it.