. . . He said one of the reasons is that the dipstick is one of the only sources of dirt in an otherwise clean transmission. Just a bit of dust or lint on a rag used to wipe the fluid off the dipstick is enough to snowball into a much larger problem down the road. The engine lubrication system is designed to deal with lots of soot and junk... but an automatic transmission is a much more "sterile" environment. According to him, the sealed transmissions should last much longer.
LOL!! The main reason why automatic transmissions fail these days is that they have design problems (such as using el-cheapo plastic parts inside) and/or can't handle the torque put out by the engine. Remember back in the 1970s when American cars had the Turbo 400 (GM), C6 (Ford), or the Torqueflite 727 (Mopar)--these trannies would go easily 150K miles behind big-block motors in cars which weighed over 2 tons--sure the pan started leaking right after you drove it off the lot, but the basic guts of these units were bulletproof. Now we have crappy automatics in all kinds of cars and trucks (any fwd v6 ford product, mopar minivans, etc). But I digress . . .
The #1 thing that could be done to make automatic transmissions last longer would be to install a decent filter in the pressure line from the pump to the oil cooler (usually inside the "cold" side of the radiator). I have rebuilt half a dozen automatics myself, and the "filters" used are basically to keep chunks of broken tranny parts from getting into the pump--they let all of the small metallic wear particles through, causing wear of the valves and other parts inside.
I used to work at a company which made aerial lift equipment which was all hydraulically operated, and we used 10-micron filters or better to keep wear particles out of the system. We also used ATF by the truckload as the hydraulic fluid, and all of the hydraulic component manufacturers said to filter it BEFORE putting it into the hydraulic system, as it apparently could have wear particles in it from the factory. Now automatic transmissions don't have as small of tolerances as the load-holding valves we used in our hydraulic systems, but they are still hydraulic systems, and particles in these systems cause components to wear out.
So, anybody for making a retrofittable kit to filter your ATF? I've thought about it many times but have never gotten around to it.