In most every case, it appears that the first fifty or one hundred or so (depending on store size) walk-ins were allowed into the store to buy their iPhone 4 as a reward for camping out, but most stores don’t have nearly enough units to fulfill unreserved iPhone 4 demand.
The remaining iPhone 4 units in each store are ostensible there to fulfill customers who successfully pre-ordered online for in-store pickup.
[Thanks to MacDailyNews Readers too numerous to mention individually for the heads up.]