Agreed. The "shipping in 4-6 weeks" just after a major product announcement is pushing it. They should have waited another few weeks to announce it and have it ready to go within a week.
With such a long shipping timeframe, perhaps one of the reasons you don't see demo models in-store is for staff to avoid obnoxious questions like, "Well if you've got demo models, why does it take a month to get my hands on one?" or "Can I pleeeeeeeease just buy the demo model?"
At the same time, having previous-gen product in store just after a major announcement is embarrassing, and would probably raise a lot more obnoxious questions as well.
I now understand and appreciate why one's of Apple's previous keys to success was being able to get new products to their customers as quickly as possible after they are unveiled.