A checkbox is implicitly required. It cannot be in an unset state. Therefore showing it as required is illogical.

Okay, that makes sense but it did make me question if I had set it to be required with the asterisk not being there as with other required fields. Pretty sure I can leave it as N/A if not required but as a visual indicator I think the asterisk may be useful but I agree that it isn't logical.

Ok so this is a very quick screenshot of adding a catalogue entry, with 2 tick fields. The first is set to required. The second is set to non-required.
You can see neither show as required on the form. The first is implicitly required, there's no way for it to not be set. The second obviously won't show as required due to being set non-required.
I agree it's inconsistent, but I do think it's the right way to do it. I've added a note about this in tut_fields.

I could conceive of another interpretation of 'required' where you have to check the checkbox (tick the tickbox). That would be used for declarations. I don't think that's something catalogue fields should support though.

(Click to enlarge)

Yes, I see what you mean now, it makes no sense visually or logically to have the required asterisk on the 2nd instance of your screenshot as it can be left unchecked. Sometimes my brain lets me down :P