One distinct advantage of selling CD quality 16/44 [or even high Resolution, eg. 24/96] WAV files on a USB stick
[or memory card]
is that the buyer then has all user flexability to burn to CDs or convert to MP3 or apple format.

The disadvantge is the music is even easier to copy and pass on freely to other people.

That is probably the main limitation on the USB stick being used more as a sales media
by major record lables.

They already made big consumer unfriendly mistakes with copy protection software on CDs & DVDs.

Trying to impose copy protection on yet another format, USB sticks,
is probably one more potential losing battle too many for the record companies.