Airplane mode status and Wi-Fi status are separate statuses. Airplane mode can be on and it tells you nothing one way or the other about the actual state of Wi-Fi. This ultimately comes down to some Kindles being like phones and having more than 1 radio where you may want airplane mode on except for the Wi-Fi radio if you plan on using in flight Wi-Fi.

Airplane mode is a convenience to conserve battery during a flight. If you judge it by how well it acts as a universal radios on/off switch it will measure accordingly.