There is many reasons, the general look of tightly feathered birds, some standards call for barbless down feathers. Plus like you say it is helpful in the warm climates of asia. And tight, hard feathers are helpful in combat.
I ask because about a quarter of my oriental chicks seem to have some form of recessive slow feathering gene. I have been trying to breed it out but it keeps cropping up. Its even showing up in about 40% of my grades this year.