I like the model T analogy as well; the Ford T enjoyed a well deserved reputation for being incredible tough, easily maintainend, cheap and long lasting (just like derailleurs ), unlike its now forgotten fragile, expensive, overcomplicated, high maintenance competitors.

You show several basic misunderstandings here;
All those problems about shifting problems are caused by cheap cable housings and cheap shifters; they are totally independent of gearing systems. All indexing are placed in the shifters, and not in the derailleur, nor inside the internal gear hub.
So internal gear hub systems needs cable adjustments too, or they shift badly, no advantage there.

And lets discuss rear derailleur maintenance; this almost mythical difficult job requiring arcane knowledge and skill, and that turns people into using internal gear hubs. Lets look in the Shimano service manual an see what complicated procedures we must follow; Oh here it is;
Squirt some lube on the pulley wheels, and some oil on the joints where the derailleur moves. Clean with a rag afterward.
That's it! That is all the maintenance a rear derailleur needs.

Steel? Rust? If you compare $5 cheap, stamped derailleurs with $150-200 internal gear hubs then perhaps. I don't recall to ever have seen a derailleur of even moderate quality that was destroyed by rust, even though the chain was rusted to a solid mass. The reason is of course, that there few parts on a >$20 derailleur that can actually rust; the pulley wheels are made of plastic, the cage of aluminium and the springs of stainless steel. Some derailleurs on abandonend bikes may appear to be rusty, but this is just rust from the chain that migrated unto the derailleur. Just try to scrape the rust of, and you will see.

(Just took an inspection round in our street, checking out old bikes with rear derailleurs (down tube shifters, Shimano Exage EX stuff). They were all dirty but scraping on the derailleur housing quickly revealed nice and shiny aluminium underneath even though the stuff must be more than a decade old.)

What you say is, that cheap, unmaintained Wallmart bikes often are broken an unrideable. I agree. However, if these kids were given decent bikes with derailleur systems in the same price range as an internal gear hubs like SRAM S7, or Shimano Nexus, you wouldn't see these problems. Besides, please do your kids a favor and foot the bill for their bicycle maintenance. Give them the feeling that it is nice to ride a bike.

You can't be serious; looking down your chain to see if it has shifted? No one needs to do that, even with downtube shifter technology from 15 years ago.
Difficult to operate a shifter? Again, you can't be serious; brifters and trigger-shifters are both very simple to operate; you just click and shift. A rear sprocket shift is usually done in a 1/4-1/3 pedalarm revolution in high speed.
Anyway, SRAM makes grip-shifters for rear derailleurs too, so no advantage for internal gear hubs here.

Do yourself a big favor; arrange a testride on a modern city-bike like a Specialized Sirrus. Pedal fast, and enjoy the crisp and incredible fast shifting, even in high speed.

{snip]
I hope I have demonstrated that your conclusion are based on false premises.

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Regards