IIRC not all deluxe sit-down models are force feedback. I might be wrong but if you have a force feedback joystick then you need the force feedback with the servo motors and if you have a regular joystick then they are interchangeable.
I can look at my upright but if I remember correctly they are just a standard heavy duty metal body pot.
There is an adjustment board on the stick that (probably?) makes it so that you can use various value pots.
No, you're actually not wrong. Sega also sold some 50" sit-down cabs with the big bench seat that fits 2 people that did use the same stick as the UR.
I think they were factory-converted Ocean Hunter cabs that didn't sell...
The "real" DX with the force-feedback stick has the small seat with the two pink fluorescent lamps mounted on the back of it.