Another idea is that they have something we haven't seen before (not just an enhanced product) waiting in the wings. The iPod was supposed to be a starting point for Apple in the 'digital lifestyle' product line. Apple overestimated the sales potential of the iPod, but still turned a profit with them, as well as the stores selling 20 iPods a day during the first week, which isn't all that bad for a Mac-only, 400$ product.
Now, at the very least, flat-panel iMacs are a certainty. Apple has been wanting to do this (CRTs are hell on the environment, and Jobs being an environmentalist and all) and with prices for LCDs being what they are at now, they can finally make the switch over to a true LCD-only company.
Also, fast-speed G4s (or possibly G5s are coming to mind because of the banner, although I am not holding my breath) like everyone else said, that will close the gap. I am hoping for 1.6Ghz machines, but my mind tells me only 1.4Ghz will actually arrive (G4 OR G5) until mid-year. I am also partially expecting a new mobo design with this 'HyperTransport' 400Mhz bus and DDR RAM Apple helped invest in awhile back. The G5s were rumored to have it, and either way, this would be a great boost to the power of even current speed PMG4s.
New iBooks/PBG4s? I doubt it. The iBook might get tweaked, a larger display might be nice, but I doubt it. Wait until MWSF for those two to get their yearly overhaul (1Ghz PBG4s would be nice then...)