I don't doubt that properly set and controlled a/c is a good thing, but I've been on trains (sorry I'm not au fait with the various numeric descriptors yet) where people were unpacking their suitcases to get their dressing gowns and socks out, as it was so perishing cold.
This would have been an ATW train, and on another occasion people were complaining to the guard and trying to move seats because they were sitting in an icy blast.
Even today I was glad to reach my destination, as any longer and I'd have been uncomfortably chilled. It's probably okay if you're only going a short distance, but for a couple of hours journey you do tend to notice your body temperature dropping worryingly.
Maybe it's a ploy to sell more coffee!