The bolt in a DI gun gets much hotter in operation than the bolt in an OR gun, too hot to handle, which can be a deal-breaker if for some reason you might need to do emergency maintenance on the bolt (probably not very likely).
I think Stoner pretty well knew what he was doing, when he went to DI. You obviously avoid the piston rattling next to the barrel.
Stoner wasn't married to DI. He built the Armalite AR-18 as a piston-operated advancement on the AR-16.
EDIT:
If my media tag for the video isn't working, it's
here.
I have pulled the BCG from my DI AR after some pretty long strings of fire and it was never too hot to handle while the barrel would blister skin.
The video shows how well the DI AR works and also shows how poorly most in the firearms industry shoot. As the video goes you can actually see the shooter improve his reloads and become more efficient at keeping the gun running.
I am always amazed at how well designed the ergos are on the AR-15 and it seems possible (based on the AR-18) that Stoner got somewhat lucky with the AR-10 and AR-15 in this respect.
This really is why all the other pretenders like the SCAR have such an uphill battle in the Carbine Improvement program. If the contenders keep the inline recoil then it is just another AR and if they try and drop the stock to look different then the gun will never shoot with the AR in the hands of someone who has the slightest clue.
