I was thinking the same thing, but there is one thing in the way.
Well, three things actually... the current Powerbook range!
They aren't going G5 any day soon, and the G4 is doing well to be at 1.5Ghz at all on the current die size. They have also been updated relatively recently...
So where does the iBook go?
They already have decent enough graphics, a superdrive option, 1.2ghz speed, slot load drive...
I am at a loss as to how to improve them at the moment! They can't up the processor or specs without really canibalising Powerbook sales...
I am a prime Powerbook customer, but about to buy an iBook!
Then again, hope springs eternal, and Apple may surprise us all round!
Either way I'm probably buying on Thursday!