That comes from people who grew up around copper plumbing and nothing breaking that solid copper path. The day they sold the first water filter or water softener that became obsolete thinking. When utilities went to non-metallic pipe the code had to change.
The earth is still a significant return path to the main distribution centers though, anywhere that they use wye distribution. Even if your local MV > 120/240 transformer uses a delta primary, you still have a percentage of your neutral current returning via the ground electrode. Dr Ohm says he has to be so.
