Hey Stringreen,
You are correct Vandersteen has models with built-in active subwoofers. Many other companies build their own subwoofers to integrate with their own speakers.
However, one of the innovative factors in the new NSMT System Two speaker is that Erol is one of the few designers who is brilliant at designing band-pass active subwoofers, instead of port loaded or acoustic suspension that has to be controlled electrically with either the cross-over or digital shaping. I get into a lengthy explanation of why band-pass designs are rare and sound significantly sound superior in many ways to the normal designs mentioned above in the review.