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Yes, I'm sure you're correct, the axle should not 'creep forward' and even if it did it would not move evenly, but jam as mentioned above.
On your second point, I think there's something in what you say. Nowadays very few people actually ride their bikes to races and, as you say, we have multiple bikes.
However, track ends must give more scope for chain adjustment, so you can have a bigger difference between the sprockets on a double sided hub, which might be useful to an ambitious time triallist riding out to a flat course suitable for a big gear. Is there anyone who would still do that?
clubman-
Some people used to go out to the Catford and Bec hill-climbs on 42/16, then ride the hills on 42/20.
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might be useful to an ambitious time triallist riding out to a flat course suitable for a big gear
If you're fit enough to push a big gear in the race, you're fit enough to push it on the way to the race. Most people aren't going to have to do anything worse than the climb from Marlow to Handy Cross, and you have to do that on your race gear 🙂
If you're going back to the olden days when we carried our sprints, a lower gear for the travelling bit would make sense, but I'm not that old so the only time I've used sprint carriers it was on a bike with a dérailleur anyway.
lesterama
gbj_tester
I guess the main advantage used to be that you could ride your path/fixed bike on the track when you took off your brake(s) and guards. Nowadays we N+1 it.