Goodlistening, you wrote in response to my post.
"I would guess that over 50% of "audiophiles" have not personally swapped out a cartridge. It does take a steady hand and when you get up in age and your cartridge is north of $500, it just makes sense to let someone else who is skilled at it do it for you."
I have no idea whether your estimate of the percentage of audiophiles who do not mount their own cartridges is correct or even close to correct. My post had nothing to do with that topic. I was saying, and am saying, that one reason why Rega may purposefully limit the adjustability of their tonearms (VTA, alignment, etc) may be that they do not trust their customers to do it correctly, which has the secondary benefit (for Rega) of pointing their customers at Rega cartridges, which are in turn designed to mount on their tonearms. A tertiary benefit is they avoid unfair criticism from customers who have made an error in cartridge mounting that causes bad sound; they "idiot-proof" their products, in other words. I don't know that this is the case, just guessing.
You also wrote, "The PSU is the motor that drives the platter to go round. It can be inside the plinth or a separate gizmo as you called it. Hence, if your motor dies, you unplug the PSU and replace it." This is not quite correct. An outboard PSU for a belt-driven turntable does not contain the motor; it typically contains a specialized AC regenerator circuit that permits the user to modify the voltage or current which the PSU puts out to the actual motor. The motor of course drives a pulley which drives the platter via a belt. PSUs became popular only in the last 20 years or so, to counter claims that BD turntables do not maintain constant speed in the face of stylus drag and belt creep or slippage, which phenomena can be quite audible by altering pitch, especially on piano music. These days any self-respecting (expensive) BD TT is bound to include an outboard PSU, and for those that don't, there are numerous aftermarket devices that perform the same function. Using a PSU has the additional benefit of blocking EMI from the motor which can otherwise get back on the AC supply for the other components of the system, which can manifest itself as noise.
In your discussion of VTA, you refer to "needles". What you see poking out of the business end of a cartridge is the cantilever, not the needle. The stylus (needle) is a tiny thing mounted on the end of the cantilever. VTA is important because the angle of the stylus to the groove affects what parts of the stylus are in contact, which in turn affects tonal balance. Most people start with the top of the cartridge parallel to the surface of the LP. Then they adjust VTA up or down (at the pivot) to achieve what they perceive as proper tonal balance. This is why you have to buy shims in order to mount a non-Rega cartridge on a Rega tonearm, often.
