I've found that these styles don't differ all that much really. The gi changes things here and there, but otherwise there is plenty of overlap.
For instance, shoot-wrestling and submission grappling are essentially one and the same. Many of their techniques are common to BJJ and catch-wrestling. Sombo derived some of its techniques from catch-wrestling as well. Anymore, it's all a mix. Seems like the stylistic lines are blurring at an ever increasing rate. But are they really? Could that be just a misconception?