Globalsmack that is nothing more than conjecture.
If you buy a proper m16/m4 upper with m16 bcg and oil it you'll never have problems with a DI gun. Pistons add extra weight, extra proprietary and expensive parts, and don't fix anything. Your barrel will be useless before the carbon fouling in a DI gun can start causing any problems. Piston AR15s exist because some complete fool attributed the reliability of the AK design to its piston operation and not the fact that it's crudely made with very high tolerances between parts.
"From my cold, dead hands!" - Charlton Heston