CHIME NOISES INTENSIFY
Yes! I've always wondered this as well.
My thinking is that since airbenders aren't really represented a whole ton in either series that it just hasn't really been introduced since each team avatar hasn't met a ton of airbenders.
Remember though, in the original series, metal-bending/blood-bending were invented/known only to very few while manipulating lightning was only taught to the royals of the fire nation.
Plus, the thing mentioned above about how airbenders are pacifists. I'd never thought of that before!
RANDOM FACT OF THIS POST: Dee Bradley Baker, the voice of the animals of the avatar world also voices the nefarious Tarrlock!