How stupid about golf are you? First, you wondered why he didn't just putt out. It just doesn't happen that way. He could have done it but just did the typical thing.
Sure, I heard the announcers say they went out of turn and knew it wasn't a penalty. So what's your point?
The PGA doesn't give a rat's a** if Zach wins or not. If the rules dictate he was disqualified, that's what would have happened. Would have been similar to Dustin Johnson at the PGA a couple years back when he grounded his club in a trap. Knocked him out of a playoff for a major. You don't think that ruling took some balls? When a rule has been obviously broken, there is no wiggle room in golf. It's definitely harsh at times. This one was actually very obvious when watching the video.
As for Zach's caddy, he was busy raking the the trap after Zach hit out of it and didn't see Zach move his mark. If you look at the video, Dufner's caddy actually cleaned Zach's ball after he marked it since Zach's caddy was raking. So in this case, you really can't blame the caddy but ordinarily they would be watching for something like that too. I'd guess he might have caught it when Zach was ready to putt but didn't know. I'd also guess those two won't ever let it happen again.
Zach screwed up and admitted it. That's not an insult to him. I'd guarantee you had he been DQ'd because of it, he'd have handled it with class, as usual.