I agree that the line between casual and smart-casual has been blurred. I just got off the Millennium last week and there was little difference between smart casual nights and casual nights.
In regard to formal there were VERY few tuxedos on the three formal nights. There were a few more on the first night but less on each subsequent formal night. Most men were in suits or sports jackets and slacks. The Asian itinerary may have been a reason for the few number of tuxedos.
Take Dave's advice and pick up some Docker pants and polo type shirts for your son and that will cover casual and smart-casual nights. A shirt and tie will probably be fine for formal nights.