And if you read my post, you'd see that it wasn't the non-upgradability that was the problem, it was the combination of non-upgradability (lack of PCMCIA in iBook and no PCI in iMac), non-expandability (using USB 1.1 instead of 2.0), and lack of support for older computers (AirPort not sold, only AirPort Extreme). If any of these had been done differently, then I wouldn't be bitching. Hell, the one that pisses me off the most is that used AirPort cards on eBay sell for twice what a new AirPort Extreme card goes for.
By forward compatible, I meant that if Apple had used a standard connector, like PCMCIA, then I could easily put in either an original 802.11b card, or upgrade to a new 802.11g card. The machine would be forward compatible.
All notebooks, including your PowerBook use PCMCIA, and the iBook has something like that, so I think it's reasonable to be annoyed that they didn't just stick with the standard.
Or just stick with a standard PCMCIA slot, and use USB 2.0 when it was originally available, instead of intentionally crippling the hardware...