It was announced that Apple has entered into a contract with Freescale [Motorola's spin off of it's microprocessor division] to buy G4 CPUs through 2008.
Many reporters are saying that Apple is expecting a slower transition to Intel Chips than first realized or that Apple may even be hedging their bets a bit.
People - Applecare is 3 years long. If someone bought a G4 based Mac today - the AppleCare would not run out until August of 2008. Apple's current plans are to sell PowerPC Macs until a completed transition from PowerPC to Intel in 2007!
I see this as the only reason - in fact, I see Apple making another announcement in 2008 to extend contracts for G4s another 2 or 3 years (possibly 4) just to keep Applecare and parts inventory. Apple is required to keep parts for 5 years and doesn't end of life / stop support completely for computers until 7 years past introduction.
Here is the official agreement and filing with the Securities & Exchange Commission.