The latest Dura Ace version (7900) doesn't offer a triple and the previous one (7800) had an odd-ball arangement where the granny ring bolted to tabs on the middle ring. So, for a real triple you are limited to 105 or Ultegra.
Differences are weight, minor cosmetics, bling and, of course, cost.
Yes, all of the external bb cups interchange. Chainrings do interchange also except for the Dura Ace 7800 granny.