I don't know what a "Luddite" is but when I find out, if it's bad I'll shoot you in the pinkie toe!
Pete, adding a piston to the AR system does nothing for it's performance. It adds weight and parts that may fail. I get a lot of guys through with POF/LWRC and some add on piston systems and they **** themselves when the round count starts to go up, usually parts that DI guns don't even have. Keep it simple and there isn't much more simple than DI. Knights has the right idea, small changes that enhance reliability without trying to be the next "big thing". Larue has also done some amazing **** with their OBR series but guess what, it's still a DI gun.
A well lubed mil spec DI gun will run just as long without cleaning as the best piston AR's. Piston's affect accuracy (more moving mass) and everything you can do to reduce weight on a picston gun, you could also do to a DI.
I think Pat Rogers has a DI 14.5" mid length BCM (mil spec) that's had over 34,000 rnds through it without cleaning. He just keeps lubing it. Perform regular maintenence and they'll run just about forever.
So why do we need a piston? Kinda a fad. Like a GSXR1000. Every homo needs one. (not that there's anything wrong with homo's, just homo's who ride GSXR1000's)