Call of Duty and simulators such as ArmA/Operation Flashpoint take different kinds of skill. Tell both a professional ArmA player and a professional COD4 player to beat each other in their own games... both will lose on the other player's game. You can show off whilst playing any game, in fact; there's a lot less room to 'show off' in a simulator given the nature of the game.
Cool kill, but was it done in a pub? :/
To be honest the Call Of Duty games are probably the easiest FPS games you can play. Sure simulators are different but they are also similar in the sense that they are both FPS games. Both games do take different kinds of skill but the amount of skill needed to be good at Call Of Duty is nowhere near the amount needed for a simulator. Call of duty is basically this, run around the map like a mad man, spray like hell, drop a claymore, win game. It is a very basic FPS game. Now something like ArmA/OFP/AA is like this, use tactics and teamwork to find the enemy, once enemy is found find the best possible way to take down the enemy without being found, adjust aiming depending on enemy's distance, stance, and movement speed, take down the enemy and quickly re-locate without giving your position away, repeat. That's just killing one enemy, you have to do tons of other things while playing too. To sum up Call Of Duty, it's a frantic, unbalanced, clusterfuck of a game that requires little patience and team work.