Key factor surely is these are electronically controlled motors. What the speed pot does depends on the motor type and how the board is set-up. Not much consistency in it when the technology is looked at closely.
Motor types that can be speed controlled are managed in different ways. Brushed motors are different from induction motors, single-phase motors are different from three-phase motors, and brushless are different again. Some types (like three-phase), get hot when run slowly, and the problem is much worse if the motor is cooled by an impeller. Brushless motors can safely be stopped as an active brake, and brushed motors are relatively tolerant of slow running. So on the basis the operator doesn't need to be a motor expert it's best for the electronic controller to stop him cooking a motor he doesn't understand.
Nothing to do with brand names, quality, advertising or country of origin, it's just that machines are what they are. And what machines are is usually a compromise. Good old Myfords run on single-phase motors that can't be speed controlled at all. Myford's solution is mechanical: belts, pulleys and back-gear, which means a clutch is highly desirable. It was the best compromise in 1947. More options today: a WM180 applies a different solution that I argue is generally more convenient than Myford's mechanical system, but not a complete alternative. For example when torque is vital.
Just a guess without seeing the circuit, but I suspect Bosun's lathe runs fast because a trimmer pot on his control board needs adjusting. It's purpose is to set the minimum sensible speed at the factory and the setting may have shifted in transit. Or it was done on a Friday afternoon!
Bosun probably demonstrates a logic error too. He assumes lathes are mis-advertised because his particular machine happens not to meet meet the spec. Given there are thousands of the breed about, it's more likely that Bosun's individual machine is wonky than a reputable UK seller is misleading everyone. Don't assume all Vauxhall Corsas are rubbish because mine got a puncture!
Dave
Edited By SillyOldDuffer on 22/07/2021 13:55:58