I think perhaps the newb might not know that FN and Colt are cranking out M16's and M4's as quick as the machines and workers can get them assembled. Being involved involved with the Military & LE Class III trade for some 10 years now, it is still interesting (atleast to me and to this retro forum) that there are in fact firearms still being used by our armed forces that are some 40 years old! Not all our "War Fighters" have the new front line guns and gear that people "think" they have. I know of 2 Mil Inventories that have firearms such as the one posted en mass. That being said, the men & women of our military utilize what is available and make whatever is given to them work.
On a side note, a nephew just went to ROTC summer camp at Ft Polk in Louisiana. During their firearms sessions, they were used M16A1's....they had a Ma Duece full of them. Most had just the handguards changed out, still with their pencil barrels. One according to an interested soldier (and his trusty iphone) turned out to have a lower dated 1969 ! Wow !