"I wonder why they didn't use a ball detent that is secured in the top of the yoke, and locks in a small cavity in the bottom of the barrel lug.....the sort of lock used in the PPC revolvers and other revolver barrel combinations when the front locking lug is eliminated?"
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I'd like to know the answer to that also - I bought the gun mainly to have an example of the new lockup. Having both types, it seems like this style would be more expensive, but I have zero knowledge of manufacturing. If it is more costly, then I would think it must have an advantage in strength and/or longevity.

It's amazing to me that S&W can do all this at a price I can afford. It's easy (and common )to dismiss their efforts with "it's just fancy machines and MIM", but I think they put forth a lot of engineering and design effort to make a great product.