I think one of the major things that does separate one martial art from the next are the nuances with how each style trains their bodies to do the same techniques. It's in these ingrained responses and actions that are imbued to the fighter through long years of continual practice, combined with the particular type of conditioning that you do, that will determine how fast, how hard, how soon, and how long a person will be able to do anything.

for instance look at this video at 4:00 and again at 6:00 and you'll see what I mean when you analyze the results. There's more than just these two guys, but these guys are doing the same technique, with roughly the same body types, but with glaringly different results. Basically the same kick, delivered almost the same way, but not exactly. Relatively the same speed, but the amount of force difference is staggering. Could it be argued that he's just a better kicker? Sure, but that's the whole point right? His technique is slightly different in posture and his posting foot during the kick. His style gave him more power in that particular instance between those two men. However the mt fighter had more control and was back in guard faster and steadier.

http://www.youtube.com/watch?v=Gnu94B6Edrs

I know I didn't use any gongfu in my example, but this video was convenient and the second roundhouse video I found and I'm lazy. In my opinion however, it's also part of the reason why gongfu is gongfu, karate is karate, muay thai is muay thai, etc. aside from the more spiritual and cultural trappings.