almost all of the shots on players in that last left 4 dead video are headshots. here, i'll point them out for you:
0:03 headshot, 0:20 headshot, 0:29 headshot, 0:33 headshot, 0:37 headshot, 0:41 headshot, 0:47 headshot, 0:51 headshot, 0:57 headshot, 1:00 headshot, 1:02 headshot
the ones that pounce in the air are players, the ones that just run around like retards are NPCs.
regarding that quake video: so does everyone else since aim prediction requires fast reactions more than raw control. the fact is that almost nobody else can get 70%+ accuracy that consistently on that many frags and most people use low sensitivity