what the hell? As I thought DSC was just a communication standard. Then I see all several DSC units with GPS or GPS input... and wondered why.

AIS is an automatic transponder that sends data without human input.

The thing that blurs the line are functions such as what Mark mentioned above... being able to manually poll GPS data from a selected remote source. AIS does the same thing, only automatically.

As you say, this is a side benefit of more advanced DSC units, not the original intended function. But you can see how one may be confused, by these nearly identical functions.