Tony has it right on both counts - the collectors want models that fit with their pre-existing collection scale. This for the most part, will be 1/32nd, since prior to the arrival of Mr Polk and his ‘wow-factor’ scale, large scale standard-gauge models tended to conform to the Gauge 1 standard scale of 1/32nd.
However, in recent years, there seesm to have been a major shift toward 10mm to the foot scale here in UK - something that has been taken on board by an increasing number of modellers and suppliers - TenMille is just one such brand. The various Barratts make their kits in both scales, as does Keith Cousins.
As for the odd-scale Aster models - namley 1/30th-isg, well that is easy to explicate - Japanese Railways run on Cape Gauge track - 3ft 6in - and are therefore ‘scaled’ accordingly. The wonderfully impressive C-62 ‘Hudson’-style locomotive in 1/32nd scale looks VERY small indeed by comparison with even a K4, as, of course, it is in reality. In fact, it reminds you of the kind of loco you might see running on the Romney, Hythe & Dymchurch railway, rather than the mighty little loco that it really is. There is also the pressing matter of the track - Cape Gauge is only around 33mm in 1/32nd scale…almost the same as 0 gauge…clearly such a little loco would need its own track.
It would also, cough cough, look less impressive than a corresponding Western model of the same kind of locomotive - say, the CPR Royal Hudson. And THAT would never do to the face-saving Japanese railway-modeller.
In Japan, only the Shinkansen runs on what the rest of the world calls standard gauge - 4ft 8.5in.
tac
Participant Principale - Fedération Amicales des Ballons Gonflables et Dirigibles Sauvetages de Mont Flarpe