The web site says that neither class of service nor Skywards status gives extra allowance beyond two pieces on U.S. flights.

What's the rationale for this? Do they ever make exceptions upon check-in? (When I checked in for my short-haul flight to DXB, with a stopover en route to the U.S., the supervisor told me that they would likely grant me another piece as Gold in J, but of course this isn't definitive.)