I'll admit those DD guns are Perrrrdy!
And apparently they're pretty durable which is nice.
But in my opinion that kind of testing video is all flash.
First off, the sand is the wrong kind if you're trying to simulate Afghanistan. Apparently Afghanistan sand is so fine it's more like a polishing grit. I'd want to see it subjected to at least 4-5 mags with a new exposure to sand between each one.
The mud was a decent test, but it's obvious that you can't expect the firearm to continue functioning after a thick oozy coating of mud with no rinsing. If you could test other guns in exactly the same test, then you could tell whether this was a specific failure of the DD or if that's a typical response to that environment.
The drag proved that a gun aggressively exposed to dirt and rocks could jam if gets inside. I bet most ARs would have a similar response, but designs like the Tavor might not since there is not the same level of exposure to the environment around the bolt carrier. Again, test other guns to identify whether the test has similar results to different designs.
The frost test was poorly done. In the end, all it proved was that you could cool it down and when it warmed up it would still work. They should have thought ahead and tried some dry lube prior to frost so they could fire it when cold. Personally, I'm not sure it's worth testing for cold temperature unless you're testing it in the winter where everything, including the user, is subject to the same cold (ie: -40 in winter). That way you can find out whether or not the user can actually use the gun (which is the important question) Also you can then find out how durable it is in that environment since it could be dropped off a truck and bounced off rocks at -40 too.
The explosion was a good question, but really, if the user ends up in little pieces, why do you care if the gun sorta survives? I suppose if you're a military and want to minimize loss of equipment, it might be some advantage, if you have anyone available to recover it who's not busy with a firefight or medical response...
Just my $.02
Still, who doesn't love seeing destructive testing...