G4 Sawtooth and later will take airport cards, but need no adapter.

the adapter, however is used for the new-world imac g3's as they needed a riser to connect to the cards.

All retail airport cards shipped with the adapter, which means a LOT of these adapters were tossed out.

Airport Extremes were a modifed mini-PCI interface, and all systems supporting the card had the slot built in.