The thing is, what else could these other Kultures be that aren't already existing as Oddboyz or special organizations? Good with vehicles? Those are just Meks. Sneaky? Kommandos/Blood Axes. Better organized? Stormboyz. Good with a certain type of weapon? Tankbustaz/Burnas/Lootas, etc.
Plus, one of the cool things about Orks in previous editions, and still somewhat present in the fluff, is that they don't tend towards mono-clan armies. Sure, they'll have a dominant one, but there'll be a few hangers-on, some Goffs following the Bad Moon Warboss along waiting for a good fight, some Evil Sunz wanting to ride in that Bad Moon juiced-up Battlewagon, and some Deathskulls skulking around waiting for everyone to be distracted.