I would assume that the guys who were firing both weapons were at least competent marksman, the test firing was done at Piccatinny, using Army owned weapons. It has been a few days since I saw this but I do remeber somebody firing a weapon with thier finger so far through the trigger gaurd it lokked like they were wearing the rifle as a ring, I doubt that makes for good marksmanship.
As far as how Ak's stand up to full auto fire, they do eventually beat themselves to death, some are made better than others, but after alot of FA use they end up with major problems. The stamped models end up with wallowed out FCG and trunnion rivet holes, Milled recievers after much abuse start to develope stress fractures in the same areas. THese weapons were never developed to be fine examples of craftmanship, they were engineered to give the common peasant/conscript more firepower than a Mosin Nagant, that is all. AK's were not dedisgned to be tack drivers, or submachine guns, the Soviet Union already had weapons to perform in these roles, the Soviets liked the idea of the SKS rifle better, but eventually adopted the Ak because it was cheaper and easier to manufacture, plus it was designed to use high capacity magazines, which at the time was seen a good feature but was not yet considered esential (remember the Mosin Nagant's and Mausers only held 5, the Garrand held 8, and even the Enfield only hel 10). The AK was actually ahead of its time, it had many features that were not considered important until a decade later, such as the detatchable 30 round mag, ability to be manufactured in primitive conditions etc.. It is a great testament to Kalishnakovs design that it is still considered an acceptable design today. The AR15 was designed twenty years after the AK. Many people wonder why so many countries used SKS's long after the Ak was invented, the truth is that SKS was considered by the military experts of the day to be vastly superior. Many Eastern countries believed the AK would be most useful in a roll similar to the way we used the M1 Carbine in WWII.