I think that perhaps there is a disconnect here as we type rather than chat
when someone on a forum makes a generalisation it is exactly that - a handle to help explain something - a way of understanding what is happening...
I doubt that anyone believes it is a scientific proposal absolute in its determination...
I am happy that there are no doubt some drivers who are very deliberate in their decisions to drive at 40mph (known as the 40/40s here as they do 40 through the villages and 40 in the 60 limits), however, whatever their internal justification, they are clearly taking no notice of other road users or the normal custom in the UK of paying some regard to speed limits - even if only to always be below them / always be above them!
The other day on a NSL road locally I came around a corner to find an old lady peering over the wheel of a fairly new e-class Merc. as she drove along at under 20mph... She may have lacked confidence in driving that size / power of vehicle, there may have been a philosophical reason as to why she felt that 20mph was a sufficient top end aim for her on a NSL, but she clearly wasn't at any point plugged into reality - a reality which says that while legally she can do that speed and legally others should allow for bikes / pedestrians / horses / etc. around a bend, the unexpectedly low speed she was driving at could cause issues with other road users and that could cause an accident. On that particular road gravel lorries are out in force doing a reasonable speed, and motorbikes and cars fly around at certainly up to c. 80mph - now of course none of that is a justification for saying that she should / shouldn't decide to drive faster / slower - but she was clearly in a little bubble of her own and totally unaware of anyone else... I suspect you could have marched a line of Fresian cows across the road in front of her and she wouldn't have noticed! And I had plenty of time to study her until we were finished on that long straight (cars coming the other way) and on the next I was able to pass her... And she is not unusual around here...
Alasdair