It appears to me that the differences between superjovian planets and small companion stars are more one of degree than of kind, i.e., is there some kind of dividing line between the two classes, or do they merge imperceptibly from one to the other?

If there is no fiundamental difference, how do the eccentricities of small members of binary pairs compare with those of exoplanets? What I'm trying to get at is, are there fundamental differences between binary star and exoplanet formation processes, and do these systems tend to evolve differently? Three-body interactions must be quite common in planetary systems, but I thought they were very rare among isolated stars.