"If there is absolutely no point what so ever in 192Khz, I struggle to think why it has been invented. "
Two reasons off the top of my head:
1. Marketing. Instintively, bigger numbers are better on a spec sheet. We also tend to assume that if something can 'do' 192 then it must be able to 'do' 44.1/48 better. Not necessarily true.
2. The increase from 44.1 to 96 demonstrably showed improvements in the past. So, we assume, 96 to 192 must also be better? Again, there's no scientific reason it should. The anti-aliasing filters will be way out of the hearing range in both cases. Plus, the damage done by brickwall filters to enable 44.1 in the past meant that 96 sounded better. Today, the filters are quite a bit better and not the problem they once were.
Some people record in 96 because they feel they get a better result. Most people don't because either the difference is too small to bother with or they can't hear a difference with their converters.
I haven't met (or read about) anyone who bothers going to 192. Sure, there may be someone who feels they get a better sound but I would be sceptical that any differences could be heard in proper listening tests when comparing 96 and 192. In fact, I have never heard a quality difference between 48 and 96 (I work in post, hence the 48) using the various converters we have. These aren't high end but OK - digidesign 192s, Apogees etc. I am convinced I can hear some differences sometimes, but I couldn't say which rate is better quality and the difference is not enough to convince me it's not my head. I haven't done any ABX trials, only adhoc listening tests.
In fact, I have read arguments that say the higher clocking precision required at ultra-high rates (192, 176.4) can actually degrade audio. Dan Lavry, who makes highly regarded converters doesn't even bother with 192 on his boxes, I believe, because of this issue. I'm not an expert in this area but if I understand correctly jitter can actually be more pronounced with higher rates. 192 does not move jitter 'higher' at any rate, according to my understanding. I think you might be thinking of shaped dither here. If someone knows more about this area I'd be happy to be corrected.
Spinal Tap was a spoof, guitar amps going to eleven started as a joke. Unfortunately for those of us who read marketing materials it's become received wisdom.