You normally need firmware support for WPA2. Obviously the availability of firmware is strongly linked to the hardware, and since firmware isn't open source, a

You normally need firmware support for WPA2. Obviously the availability of firmware is strongly linked to the hardware, and since firmware isn't open source, adding a big feature like WPA2 if it isn't already there is very hard. However, I believe there is also the option of capturing raw (encrypted) packets and doing all the encryption fully in software.