They're just refurbs. People bought them. They returned them. Apple sells them at a discount. This doesn't mean anything. I'd love for there to be G5 iBooks as much as the next guy, but this is not a sign that they are coming.
In fact, I don't expect G5 iBooks until at least a year after G5 PowerBooks are announced, which would put them nearly a year and a half away. You will see performance boosts in iBooks, but not G5s until late 2005 or early 2006.