For example, depending on the store and market size, a few dozen to several dozen units of each model in every color and internet-connectivity option will be allocated for purchases before 12 noon.
Once the store-specific sales number for morning purchases is hit, some stores will not offer those certain models until later in the day or via Personal Pickup…
After 12, Apple will start processing purchases conducted via Personal Pickup. The unallocated inventory of iPad Airs will be used for Personal Pickup. Additionally, the rest of the inventory will be utilized for walk-in-purchases later in the day on Friday. Apple is also excepted to stock up on iPad Air supply for later in the launch weekend and for next week.
This process by Apple is does seem designed to create artificial constraints, but more of a way to ensure that all customers, including those that reserved through Personal Pickup, have the ability to purchase an iPad Air if they come in Friday, Saturday, Sunday, or any other day in the near-future. Apple CEO Tim Cook previously said that some customers may not find an iPad Air on launch day.