FCC to regulate cable?

I've been reading about Jay Rockefeller's promised upcoming legislation against violence on TV, including programming on cable and satellite. Aside from the whole censorship issue, I don't understand the justification for the FCC to mandate anything outside of broadcast TV.
I thought the only reason that broadcast TV fell under government stewardship was because the broadcast spectrum was a precious, finite resource. Is that not true? How is cable or satellite transmission a finite resource? If it is a finite resource, is it because cable or satellite companies have a monopoly? If that's the case, why aren't laws being passed to regulate that instead of content? I really respect some of the things Rockefeller has done, but I'm not sure about this one.
I've been to places like the Parents Television Council (which was invited to speak before Rockefeller's committee), but they just seem to say that people get programs they don't want when they sign up for cable, but not any justification about why the FCC needs, or even can, become involved in this debate.
Can anyone leave a comment that would enlighten me?