This is a common comment at exhibitions, almost as common as asking if it is EM or P4!
I have a theory why S is perceived as “the right size”, and it also applies to Gauge 1 in its (proper) 1:32 format. The human eye with the help of the brain measures things via angular displacement, binocular stereoscopy and perspective and as with standard geometry is pretty good at halving angles. If you take a half, and halve it, and halve it, and halve it, you have 1/32nd of your starting point: do it once more, and it is 1/64th of the original. It therefore “fits” just right into the mind’s eye. It’s only a hunch, but there is probably a PhD thesis that could come out of it! Incidentally, this also makes the scale ideally suited to the modern computational era: two to the power 6 is 64, or 100000 in binary….
So, the fact that it suits the eye is probably why people ask if it is EM or P4 – in the mind’s eye, this is the size their 4mm scale should be!
The Erratic and Wandering Journey 
Dear Simon,
What a thoughtful and persuasive theory … especially the closing comment. I think you are very probably right.
Perhaps it is a pity that when Greenly, in association with Bing, worked out a ‘table top’ model railway size he chose to halve the existing smallest size, ‘0’ gauge, rather than halving Gauge 1? That said, when I saw a display of a Bing ‘00’ system in an exhibition years ago at Wednesbury museum (of all places) I was so enchanted I wanted to take it home and play with it! Just as well it was in a glass case …
Regards from David
Needless to say I agree with your analysis. I wonder if this paragraph should be offered as a piece of text for the revised Society leaflet?
Regards
Maurice
Thanks for the comments.
As for it going in the revised SSMRS handbook, I have no objection to someone putting it in.