Mac Hacker, ask EdX. They gave us users a Christmas present, or something, back in December of being able to change our screen names, and they may do it again. I missed it because I wasn't active at the time to ask for "arden" to be capitalized, but you never know...
Apple can already fit a G4 into an iBook, they just choose not to in order to give the illusion of a consumer line. Especially now, the G4 is fine for consumer computers, but Apple can justify charging less for the iBook better with a G3. They could fit a G5 into it when they stick one into the Powerbook, but they won't to give the illusion of it being a consumer computer, as opposed to a professional computer.
It would be like putting a V8 into a Ford Escort. Sure, you could do it, but a consumer car like an Escort doesn't need a V8 engine, even if the cost wouldn't go up significantly (though in that case, it probably would).