This is most likely how it works.
The books are complete. There will be optional material available 'to enhance play experience' offered on the DI which the owner can access by entering a license key found in the book.
Now...after discussion with my friend, here I believe is the kicker in all this.
To use the DI Virtual Game Table, you will need to actually own the book for the options you use in the online game. So, if you don't actually buy the PHB, don't expect to create a character online because your ability to create a character is most likely completely tied to the license keys you have uploaded.
In essence, WOTC has dealt with the issue of one person in a group buying a book and sharing it around the table to play or groups playing off the SRD alone. They can't control the usage of books around your kitchen table but they certainly can (and I think, will) control who gets to play on the virtual game table. You want to play prestige class X for your DI online character? Then you better have bought the book (with the license key) with that prestige class you want in it because it will be needed to activate that capability for your online character.