It's something
No they are not required i think, not sure if even legal.. Some people got the US version for their VW Golf IV and got in trouble. But not sure if a Corvette bought in Europe would still have them, i think so because they get imported an in this case you can have them since oem
They are not required outside of the US (and Canada, I think). In the EU, usually the part is still there, but only as a reflector. The bulb is either taken out or disabled.
Secondary markets such as Latin America usually see them still as they get a mix of EU/US spec cars, but the rear one, if separate from the tail light, is usually made yellow as well (Fiat 500 is a good example of this).
It's not so much a hassle to US automakers as it is to foreign ones, who have to figure out where to put the egg yolk in their cars. Frankly, I don't know why this is still a requirement.