Boss is an actual title and rank, while streetboss is a more generic term.

Numerous mobsters over time have been tagged the "street-boss" of the so-and-so organization. I believe its a generic term sometimes used to designate guys recognised as in positions of relative authority. Its a term the media seems to have jumped on.

Ralph DeLeo and Mike Sarno are two guys that jump to mind as recent so called "streetbosses", they were basically just captains but. Im sure theres more guys that have attracted the label at one time or another.