Not sure I agree with you totally there, but acknowledge your points.
My personal thoughts are that yes, the auto in the front means you have to adjust how you drive a little. I tend to flick back to 2WD a lot more than I used to when driving at speeds on the dirt roads, but otherwise do not see any real difference at low speeds.
Detroit have been building lockers for a long, long time now, and are proven bits of kit. If something 'goes wrong' then a vehicle would have to operate in 2wd, the same as any other vehicle. I personally was more worried about the air-lines, or wire getting damaged, than a cataclysmic failure happening inside the diff. I do acknowledge that both air-lines and a wire can be repaired on the fly though, and hopefully people who use them all carry a spare bit of hose etc.
Detroit might be expensive compared to Lokka or Spartan etc., but they are a whole lot more substantial than both, and a lot less expensive than ARB, PRO-LOCKER, or E-LOCKER. Last time I looked I could find one online for $699 shipped to my door.
I would think that getting a replacement locker in a remote location would mean the same (freighting one in), unless you are in a reasonable sized town, where you are right, the ARB etc. is more likely to be in stock. Otherwise it would just be a matter of limping home and sorting it later I would think.
My 2 cents worth...