You are incorrect - a music "track" consists of two separate copyright - one is the copyright in the sound recording (the audio that you hear), the other is the copyright in the underlying composition embodied in the sound recording (in other words the lyrics, the arrangement, the composition of the music).

There is no compulsory license for sound recordings in any territory for downloads or interactive streaming. You have to explicit permission from the copyright owner to make the recording available for download or interactive streaming, i.e. you can choose when to listen to it.

There is a compulsory license in most territories for the composition side, under certain specific conditions, in which an entity like Grooveshark would obtain a mechanical license for the composition from the copyright holder of the composition (usually music publishers) in advance of its public availability, and then account and pay royalties for its use. This requires Grooveshark to know the songwriters, publishers, and splits of each work, which is not something that comes from the user uploads. It may be the case that their terms of use pass this responsibility to the uploader.

In short, however, you need sets of permission (sound recording and composition) to legally distribute music for download or interactive streaming.