In regards to the above videos....... This is a matter of range and control. Notice in the WCK video that Anthony STEPS first....he closes the range and then uses a simultaneous deflection and strike followed by another strike. In the FMA video the action starts from a little further out....so there are two parries on the attacking arm rather than just one. One parry would happen AS the stepping in to close the distance. I do that with my Wing Chun sometimes as well. I consider it as "closing with some control and protection." I see it in those cases as increased efficiency from a safety perspective, not decreased efficiency as some might say because I have used an extra "beat".
Secondly, remember that in FMA everything is referenced around weapons combat. The empty-hand methods essentially derive from dealing with a knife. If someone is trying to slash or cut you with a knife you want to maximize your protection by deflecting and controlling the knife-wielding limb as you close in. This is why you see multiple beat defenses as well as even strikes to the knife-wielding limb itself. The sharp pointing thing is the main threat you have to deal with BEFORE you can do to the torso or head with your own strikes. This makes the strategies in FMA empty-hand a bit different that those in WCK. In WCK we just worry about getting past the striking hand. In FMA that striking hand is assumed to be holding a knife, so you can't just "get past it", you have to take it completely out of the game....either by immobilizing it or trapping it.
Third....FMA movements are often centered around the idea of "flow." This comes from the double stick work. Here the idea is that of using patterned movement that can be applied in multiple ways. You can do the same motions with double stick, single stick, knife, and empty hand. This makes learning much easier. You set the pattern in motion....some parts may pick up the attack and some might not. It doesn't matter, you still just "flow." If all motions connect and work...great! If one or two aren't that effective you are still covered by the rest of the pattern. Its like having a backup or "fail safe" built into the technique. To WCK eyes this looks very inefficient with too much wasted motion. But it happens so fast that FMA guys don't see it that way. To FMA eyes WCK often looks somewhat "jerky" and "mechanical" without much "flow." To each his own! ;-)
I'm surprised Joy hasn't chimed it. Many years ago Augustine Fong wrote an article for one of the magazines titled "Trapping: The Heart of Wing Chun." Fong Sifu talked a lot about "trapping." Trapping the hands, trapping the stance, even trapping the "emotions." ;-)