Edit: Hey guys, thanks for your kudos! This idea has been implemented in the new version of Spotify. BUT, they haven't yet added artwork for playlist *folders*. I've created a new idea for that, so your kudos would be appreciated over there as well! https://community.spotify.com/t5/Spotify-Ideas/Playlist-Folder-Artwork/idi-p/729671
Original post:
Currently, playlists are listed on my phone represented by a music note, and playlist folders by a music note in a box. Since playlist cover art is automatically generated and displayed on the desktop, web, and tablet apps, why do we still only see a generic music note on phones? It would also be nice to include art for playlist folders, which is not yet supported on the web or tablet apps.

Seems simple enough, and it's already like this on all the other devices, just not the mobile apps. I hope this means it's on its way?
Thanks for looking!
2014-06-03
Hey guys! This idea is now "Implemented"
In April we introduced Spotify’s new look. Now Spotify has a darker theme, refreshed typography and rounded iconography. This new design includes showing playlist artwork on your mobile as well.
Thanks for the kudos and for your idea suggestion @mdewater