When a company like CIngular or Sprint launches a phone, it is usually Nationwide. Being a long time Nextel user, when they launced a new phone it was the same day all over the country.
No way that Cingular would just launch the 8800 in one state or one part of the country, it would go nationwide. Thus the need for a butt load of devices. Each store may only get 5-10 phones for the launch with more coming in the days after.
I am sure that the phones are sent to the larger stores. These choice are made above the company store level as my local store says they do not order a new phone, it is shipped to them automatically.