I was thinking about the frustration many of us have / had with resellers getting stock before our Apple orders are filled, and I think it's a simple as the resellers will have placed their orders before we did.
Likely they were allowed to order before direct Apple customers, but that seems reasonable also. That means Apple has whatever is available to it when it decides it's launch day and if it's wildly popular they can only catch up with the production they have over and above the commitments they have made to their resellers, at least in the beginning.
That still doesn't explain why some regions have you guys reporting SG is readily available while I waited from 11 Dec until 28 Jan for my order to prepare to ship.
For that I think it's that NZ is because hubbed through Sydney, and my tracking suggests my pair waited for over 48 hours between preparing to ship to being shipped. In that 48 hours I expect they were part of a bulk shipment from China to Sydney - and possibly stops in between - and in Sydney the bulk is broken down to individual orders. That would mean they just haven't been popular enough in Australasia to get many bulk shipments against the other regions as everywhere has back orders.
I think that may also explain the colour discrepancy. I think it's almost certain that SG and Silver will be the more popular colours, so the actual colours are going to be lower volume. Assuming a bulk shipment is all the same colour, and further that a bulk shipment is quite a big number of individual units, there needs to be enough back order in a specific place to warrant the next bulk shipment.
'Course I've never worked in logistics nor was I involved in the logistics part when I worked in FMCG, so I could be miles off.