Questionat 24m V Sets aren't especially long (certainly not by world standards), it's that the OSCARs are short: the same length (more or less) as the Bradfield cars 60' suburban cars.
Is the V set long because it's narrow or narrow because it's long?
I don't think they are especially narrow either, just not as wide as the "medium gauge" Sydney suburban fleet which evolved from the Bradfield suburban loading gauge.
Compared with Nth American and European equivalent DD rolling stock, the V sets have shorter double decks, because they have a shorter wheelbase to meet our loading gauge restrictions.
Agree on world standards they (V-sets) are probably more standard, but Sydney has standardised on ~20m cars for many decades now, if not 100 years. There is obviously a reason as it costs more to build shorter cars than longer cars and you end up with less capacity. My understanding is that in order to get 5 seats across and still negotiate the tighter bends on old city tunnels, the cars are limited to 20m in length. The V sets and U sets still used the same tunnels, but their narrower profile off-set the extra length.
The U boats are I think around ~22m.
I assume that despite the requirement for a narrower profile for tunnels etc, the designers at the time were able to harvest a longer car to reduce costs per seat and also they were not compelled to comply with a standard 160m max length because the bulk of the stations served were either very short or very long to suit the long distance trains.
Overall, yes I love the V-sets. Spent 10 years commuting on them, however their slow dwell times at stations are a major issue and yes seeing wheel chairs stuck in the small vestivals out of the AC and in the noise and ancient inter-car doors means their journey's must soon come to an end. The B747 analogy used above is interesting as the B747 production will also soon come to an end with most being freighters and the last two being Air Force 1 and Air Force 2.
In reference to wheel chair access to planes. You will find most airlines have suitable systems in place to look after their disabled passengers and typically this exceeds the standard offered on trains. No they cannot simply remain seated in their parked wheel chairs in the cabin and especially for small planes with stairs access they may need to use a lift, but you are still taken care of. Due to the narrow aisles and doors, planes have to use specialised wheel chairs, but as the airlines provide all the systems in place, its no big deal and nothing like a commuter train, especially considering the very small number of disabled who fly.