Some airports, e.g. ORD (or at least it did), have special provisions for medallioned taxis to get priority access to the highly structured taxi line. It isn't just a tax on the special nature of the ride. In the case or ORD, some particular extra fuel-efficient fleet cars got priority on the generally highly lucrative rides.

There are other car services available and such, but in general airports fall under extra special taxi regulations given how much these rides rake in.