Paul, I disagree, I am not right.
It's just another way of wiring. If someone has a single bus and perhaps
a small battery backup then your way may be better. So, you are right too!
It really does depend upon your selection of wiring design, which should match
your mission. If you are strictly VFR you may elect to wire a very simple single
bus design. If you want to fly IFR and you NEED redundancy then other options
may be necessary in your design.
I wired each of my DU's to a single power bus. Each only uses one power
supply, the other two wires are snipped short and are unused. If you study
the Z-13 diagram you'll understand why I did this. I wired it for my mission.
Each of my DU's has it's own switch as well for load shedding. Lot's of stuff
to consider...
Paul's recommendation is equally applicable, depending upon your mission.