I carried an M-16 too long as well...;) All I know is that my Kel Tec SU-16 is a LOT cleaner in the chamber, cycles more reliably, and weighs half as much as AR-15s, which for my aging body is a good thing!
Not to mention the cost savings ($600+) would buy a lot of ammunition and a dozen PMAGs...
The only reason the current M-16 configuration won over Stoner’s gas piston design was cost; the military wanted something cheaper (over Stoner’s recommendations). You can get gas-piston conversions for your AR-15 platform, and it’s highly recommended if you want something even more reliable and easier to clean (less carbon build up).
I have to say that I think that is BS. Stoner designed the AR-10 in 7.62 NATO with a direct gas system and later Armalite scaled down the rifle to 5.56mm to make it the AR-15. The AR-15 is a fine weapons system. One of the reasons the Army dropped the search for a new service rifle is because AMC did a survey and over 90% of the troops really like the M-4/M-16 and gave them high marks. I guess AR-15s are the most popular platform going because they have so many disadvantages. BTW, here is an interesting quote for you. "Because Armalite has sold Stoner's patent for direct gas operation to Colt, the Stoner Weapons System used a piston-operated gas impingement system, though Stoner himself believed direct gas operation was the ideal method for firearms."