I was told thsi week (by a fellow Brompton user) that his tyres were deflating a little and the shop told him they have to be at 100psi otherwise that happens

My suspicion is that because they have started off so hard he now won't notice if a little is lost?, because he states they were correct as they haven't deflated
Unless there's something odd about the valves (I can't imagine they have 'special' valves that look the same as standard) this doesn't make sense, other than.......
The rate at which they lose pressure is likely to be higher because the initial pressure is higher, but until they reach a lower pressure (noticeable to the user) he won't err notice?