Slacker is free... not worth $10 vs free
Ok. but it is nice to have choice. Some may want to pay more to be able to rewind a song, request and play a whole album, have better radio stations, and maybe have a higher bit rate sound quality?
If you like music, $10 a month for Spotify is ridiculously cheap. It's all the music you want for the cost of less than a CD.
Or less: if a family has 3 Tesla's, a home account, a work account etc. it could be less than $3 a month for each car.