Yea, and good luck making sense of it all.
It makes total sense. The NEC allows us to use either a single 2 wire circuit, a MWBC or a feeder to feed a detached structure. When you use a MWBC or 2 wire circuit in a residential application a single pole snap switch is allowed and no grounding electrode is required. When you install a feeder to that structure then you must install a panel that is suitable as a service disconnect and one must install ground rods and use any other electrodes at the building. The grounding electrode conductor must be isolated from the neutral bar and attached to the grounding bar.
There is an exception before 2008 NEC that allowed a 3 wire feeder to the structure if there were no other metallic pathways such as phone lines, water lines etc. that went to the structure. In that case the neutral and the electrode were bonded to the can.
We are allow the 6 handle maximum disconnect rule to disconnect all circuits in the structure or we can use a main disconnect (my preference).
MWBC- no electrode but main disconnect is required- could be a SP switch
Feeder New- separate grounding and grounded conductors that are isolated at panel- electrode also required- disconnect needed or 6 handle rule
Feeder Existing - grounded conductor only- no metal pathways- electrode and grounded conductors are connected to the enclosure- disconnect needed or 6 handle rule