There is a significant difference between a data CD that contains eg 10 files in WAV format and an audio CD that contains 10 tracks. WAV can represent audio in many more formats than the fixed 16bit 44kHz PCM that CDs use for audio
CDA isn't a real file (if you can accept that a WAV file is), it's just a representation of a starting index for an audio track that programs on windows can use to instruct a CD drive to start playing audio at the right place.
Originally when a PC's CD drive played an audio CD it did not read the CD like it reads a data CD; the PC instructed the drive to play and the drive emitted analog audio. Nowadays it "rips" the audio cd and it is the PC that performs the analog conversion