Looks to me that they are saying "no neutral in with the service, no neutral allowed inside the building." Guess they don't want you to count on the loads being perfectly balanced, or using the ground rod instead of a neutral.
Keep in mind that the NEC is attempting to address EVERY scenario. For example, the mill I'm at today is fed by the PoCo with three high-voltage 'hots.' There's no neutral from the PoCo. This means that we need a transformer to 'create' that neutral.
A lot of wells and pump houses are served by 'corner grounded' 3-phase power. If you want to have a neutral in that pump house, you'll need a transformer .... even if it's a "240 to 240" transformer.
After all, the electricity can't "go home" if the neutral wire doesn't go all the way back to the source.
