The older pin style allows you to use the pins to space additional domino mortices along your wood surface. They also allow you to reference off the end of a board. The paddles will allow you to reference off the end of a board, but they will not fit into the mortices.
There are all sorts of ideas as to why the change from pins to paddles. It was explained to me that frankly the engineers found that not that many people were using the pins to reference additional mortices - the spacing was greater than people normally used, so they simplified and went with the paddles. The paddles also allow you to reference closer to the end of the board than the pins - I think. I have a pin model.
That is the major change.
Peter