It costs quite a bit to have different SKUs around the world, especially when one of the SKUs is for a major market. At some point it becomes more cost efficient to just cut out some of SKUs.
Cars are not iPhones though, and emissions control systems aren't slightly different models. In particular, Hong Kong has its own special dual-sim iPhone model that the rest of the world doesn't get. Only Apple knows what they'll do for USB-C, but they have per-Country SKUs for iPhones already so it wouldn't be out of the question.
They still try to have a limited number of SKUs. Suica (Japan) and CMDA (China/US) features are not limited to specific SKUs anymore, and the dual-SIM SKUs are available in India and China, two very large markets.