Interestingly enough the HD Sportster solo and pillion are still "reasonably" priced at $350 and $250 respectively. From a manufacturing point of view, you would think these were equivalent to our seats in terms of materials and labor. Must be something very special they are putting in the Triumph seats!
BTW: Since the solo 79-03 sporster solo racks fit our bikes, I'd bet the Corbin Sportster pillion for the same years would work without to much trouble too.