You see this is what's laughable. Some fool must of thought the M14 needed to be updated and the stoner rifle was born as something new. Why is it ok to say if you clean and maintain your DI gun it will last forever yet somehow the Piston isn't held to the same standard?
When you buy a high end piston you end up with a lot for the money. Chrome or np3 coated bolts and carriers, excellent barrel options compared to M4 spec, upgraded trigger groups, ect.
Mil spec is the lowest common ground the Gov't will accept not the high end standard for the market place. There is better stuff on the market today. Piston or not it a good time to be a buyer.