Rothwell - I see what your getting at, in describing the twist.
The amount of force required to move the cartridge sideways, to keep up with the spiralling groove is very small, albeit multiplied by the arm length.
The air bearing however is designed to keep the parts (Tube and rod) separated so they don't lock up, and can support the whole weight of the arm, many times the force applied by the cartridge, so it shouldn't be an issue.
The design used on my arm doesn't actually have a tube, its a piece of equal angle extrusion that runs on the top edge of a square profile track, that has holes in it, bit like a saddle, but it would offer similar resistance.
Coming under attack - feels a bit like that, not me personally, but the concept of a parallel tracker.
Some folks obviously feel its a Marmite situation, I don't mind that, the banter has been constructive, so it's not a problem for me.
I think people know where I stand on the subject and all seem to agree there are issues with any design.
Still, its supposed to be a thread about the merits of different arm lengths.