BTW, if one tried to convert a propane grill to use natural gas,
wouldn't the orifices on each burner have to be changed?

Yes.

This is a populuar topic here, and I wanted to say this the last time.
Not about grills but about my frien'ds GE gas wall-mounted oven: it
could be converted from NG to propane and back just by adjusting the
air intake.