Because they are clean enough to not need them. Let's see why:

Integras, all models: Small, clean burning engines.
S2k: the most aggressive I4 ever to be marketed, so it will puke extra emmissions: needs an airpump.
Domestic V6's and V8's: huge, ineffiecient engines: needs an airpump.
Mazda Rotaries: Needs fuel to keep them cool and for slight lubrication issues: needs an airpump.

Your car is too effiencient to need an airpump in stock form. That's good, because emissions inspectors willl not have to look for them in the future (hence why my '7 is almost a year out of inspection... the air pump is gone!)