That would be because Pandaria was established as an Asian-themed continent in WC3. You know, because Panda people live there.
Um, you have that backwards. The Brewmaster already had an oriental martial arts theme in WC3, and that theme was carried over to WoW when the Monk was concieved.As for why the monk is martial arts based? Because to fit the Brewmaster drunken brawler from WC3 into the theme they would have to give it some oriental identiy, which is where the kungu-fu-like fighting style came from, therefore greatly changing the WC3 brewmaster hero to fit in WoW.
So wait.... You can't figure out that a Drunken brawler from China's medieval times would have a martial arts theme?Brewmaster was based simply on drunken brawling/fighting. The Martial arts and Mist-wearing were given to brewmasters to make them into Monks for Mists of Pandaria.
The 'kung-fu garb' you speak of is basically an every-day style of clothing from China's medieval time, so no base there. Just watch any movie which is based on Medieval China and you'll see. Also, WC3 hero never ever used martial arts. It just smashed people in the head with a stick and a keg. Nothing very martial-arts-y there.
The ability Drunken Brawler, Splitting into three Kung fu spirits, and kicking ass with a staff isn't martial artsy?