My understanding is that publishers are in the box seat with agency pricing as they can control and enforce the price in a way they couldn't with pbooks. The eworld actually gives (large) publishers more control.
That's one of the scary things about ebooks and downloaded music. The owner or licensor of the copyright can reach right into the guts of your computer via the channel of supply and manage the rights embedded in 'your' books and music.
Melissa (downstairs) only buys CDs - she wants to have something physical for her money, something she can fall back on when the online world gets a bit screwy.