A bit of correction, and clarification on some above statements...
"Piston designs are being marketed right now to a cash burning crowd"
There are alot of products in the firearms world and any other industries that can be considered as being marketed to the the cash burning crowd, heck look at the thousands who buy $1300-$1700 DI colts when you can buy so many products made the same, just as good for less, and dont have pins made in oddball sizes only for their rifle.
"who are looking to get an different operating system on an AR."
Now I agree, something different, something they might like alot more. Or simply because they wanted a piston AR.
"I view it as trying to install a 350 Chevy in a Jeep. Sure, it can be done, but the question is why bother?"
This is an apples to oranges comparison, its more like having a self cleaning oven rather than one that you spend 4 hours after every big holiday scrubbing it.
"In the case of the piston, there is only at best a small incremental improvement in reputed reliability - something industry pros continue to explain has no basis in real life IF THE PROPER LUBRICATION IS PERFORMED."
This I disagree, but then again I own a piston rifle, I have seen the improvements, and the few disadvantages to comparing them.
Its funny during discussions about the advantages in cleaning a piston rifle all of the sudden the guys who said they spend 2-4 hours detailing their DI ARs because its part of the fun of them, now all of the sudden claim that they only spend 15 minutes doing a quick wipe down. Where they said you need to religiously clean them, now they claim that its not needed. Come on...
My problem with the "industry pros"comment is that the only industry pros telling you there is no advatage to the piston rifle are those selling or manufacturing DI rifles at a high profit margin. In order to be an industry pro you must be making money in that industry, not doing it as a hobby or for fun, need I say more.
"other issues seem to offset the idea that reliability is better. First, nobody absolutely guarantees it, period."
I dont know of one issue that causes a lack of reliability in any GP AR aside from a few models that have retrofit kits installed, not many, but a few. Next my GP rifle has the same warrantee that the manufacturer supplies with the DI rifles.
"considering DI guns have gone thousands, and sometimes 10 thousand rounds with only lubrication, buying a quality weapon will have more influence on reliability."
Theres a difference, the few DI rifles that have been tested to 1000s of rds without cleaning without major malfunctions have loads of oil being dumped on their bolts, and inner working every so many rds to keep them working.
Dont get me wrong, I like DI AR rifles, but they have realistic limitations, and their own gas system causes some of those problems, the same one that burns oil, cakes carbon to moving parts, and collects dirt and grit.
At one time I relied upon a DI rifle in war, it worked, but I spent time every day religiously caring for it, cleaning it. My life depended on it, to this day I clean my firearms the same way regardless because its the way I do things.
"another negative is the percieved loss of accuracy with piston systems, which is incremental and probably moot viewed from a battle effectiveness perspective. Nonetheless, they don't claim improved accuracy, just less time off target - in some cases."
This I can agree with, piston rifles make it harder to fire as accurately, DI rifles in comparison would make better weapons for a sniper, much better. Piston rifles require some practice, and some adaptation on the shooters part.
"Parts availability and spares are another issue."
Right now I can buy any spare part from Bushmaster or POF for my rifle, both have been around for a while, in fact bushmaster for at least a few decades. In fact I dont know of many GP AR manufacturers that havent been around and making firearms for a while, aside from LWRC and a few others. BM, S&W, CMMG, Ruger, H&K, have been around.
Realistically, if the guy wants a GP rifle hes gonna get one, he has his own reasons for doing it.