One of the cooler feature additions to the Mac OS X 10.4.9 update was its support for USB webcams. You can now use even Logitech webcams for iChat. David Nanian, developer of SuperDuper!, is pretty happy to leave the iSight behind.
Seeing as the iSight supply channels have dried up to the point that they’re being sold on eBay for more than their retail price, users need a real alternative. That alone may be the motivation for Apple including this new capability. It also suggests that Apple may be preparing a new USB version, or that they may be integrated Apple’s displays.
Personally, I’ve had so many issues with my iSight interfering with other Firewire devices (even when not in use), that I leave it disconnected most of the time. I’m considering a new USB webcam just to avoid the hassle.
I fixed those iSight interference problems by replacing the thin stock firewire cable with a thicker heavy duty cable from Belkin.