ACX wrote@[deleted] the playlists are more related with the queue rather than with the library, so that's because I think that the right place for the 'manage playlists' button is there.
Yes, it seems more logic to have playlist button on queue tab, but now i thinking on a greasemonkey script to add this option. I have to investigate this way. I have a little bit knowledge about greasemonkey but i would like to try it.
Thanks.