You are saying the same thing.Sri lanka is severe condition and go traffic is the worst thing for heat related issues.Sri lanka is not a desired climate with high humidity.You are making statements for japan roads.Even if you don't drive at all it should be replaced.More importanlty if you make short trips it becomes worse in the case of op doing 11000km just short trips.
Yes, traffic is hell in Sri Lanka - frequent stop-go traffic puts tremendous strain on transmission fluid when you DRIVE through such traffic. That's why you should replace transmission fluid when you DRIVE 40k kms under those conditions.
Water contamination due to condensation happens in Japan as well as SL - more so because Japan actually has a winter while SL does not. If this was a concern for transmission fluid Japs would have it much worse than us.
Even the suspension is designed specifically for our road conditions (High-ground clearance) so the manufacturer wasn't messing around when recommending maintenance intervals 
) if you couldn't find a severe mainenance schedule which explains what they mean by "severe conditions" online I'll PM you a pic of mine when I'm home
There's no way for dust particles to enter the transmission unless someone deliberately poured some sand down the oil dipstick opening. Transmission fluid filter is there to collect fine metal shavings off the transmission itself.