That lack of standardized parts thing is enough, by itself, to keep me, personally, from having any interest whatsoever in a piston AR.
The DI AR, among all of its other awesome attributes that have led to it being so incredibly popular, is extremely standardized in terms of parts fitting and availability. Not all parts are created equal and we all have preferences, but even outside of those preferences there are a <deleted> ton of other parts that will fit just as well, and function as designed, and there will be for a long, LONG time. Those parts, and other rifles that can be used for parts, are absolutely everywhere.
You know, I like my piston driven Ruger 556. It is a very well made fire arm, reliable and consistent. I like it much better than my friends direct impingment driven Smith and wesson m&p15. His also works reliably but doesn't spit brass in a neat little pile like mine does. Beyond that I like the way mine feels much better but I cant say much more than that.
It seems to me, and I chose my piston AR for this reason, that venting hot gases out of a firearms action sooner in the firing process is a good thing. Doesn't necessarily mean the other way is broken, but I would prefer it the way I chose. You can spend thousands on a DI or thousands on a piston AR. I was looking at a Daniel Defense VS. the Ruger when I bought mine, and they were within 50$ of each other where I was shopping. They were both very high quality and I believe I would have been happy with the Daniel Defense As well and may yet buy one down the road.
As far as the people that are "concerned" about parts availability, ask yourself how many other fire arms do you own that dont have a market wide standard. I own several Smith and Wesson, Dan Wesson, and Ruger revolvers, bolt action rifles of various makes, shotguns of various makes, other semi auto and single shot rifles of various makes ect...and guess what? Out of dozens, There are only 5 of these that could use parts from a different maker than the original manufacturer in the way you describe. And one of them is my piston driven Ruger. It can use most of the parts from another ar15. Heaven forbid it cant use all of them.
You know, despite that horrifying revelation, ironically enough, I don't lose sleep at night about parts availability for the rest of them! Its the darndest thing! I have had to/wanted to replace parts from many firearms, some 50+ years old, and it was as simple as calling the manufacturer, in a couple instances, going on gunbroker. I didn't have to search high and low to the ends of the earth to find that magic elusive part. I found them In a matter of minutes and they all have arrived at my door within a few days. Some I was able to pick up at local stores.
Personally I am not really worried about it breaking. If it does in the end of the world scenario, which is what I am sure some of this thinking stems from, there will be guns laying around everywhere, and I wont need to fix it. I can just pick up a new one. This concern people seem to have seems rather silly to me.
