The French Applestore has some interesting details on their website.
According to the French Apple Store Translated into English :
Using a technology similar to the iPod nano and other products to flash memory, MacBook Air incorporates for the first time a disk SSD (solid-state drive). Available in two capacities, these discs contain no removable parts and accessing data much faster than standard hard drives, which translates into a significant improvement in performance when running the computer and opening files and applications. In addition, the SSD drives offer better durability and better preserve the data in case of accidental fall.
Was Apple planning to make the SSD Drive in the MacBook Air available in two sizes? What other size should they have offered?