Firewire, even FW400 is vastly superior to USB2. USB2 approaches FW400 in raw total data, but it is nowhere near as robust or flexible. I can pull the FW cable from the drive in the middle of a copy, wait 5 seconds, and put it back, and the copy continues. That’s impressive. There’s a reason video cameras, for example, don’t xfer video over USB2. Start talking FW800, and you’re not even in the same league anymore, performance-wise. USB2 is cheaper, but it’s cheaper mainly because of sheer supply, not because FW is inherently more expensive. For general home and consumer needs, USB2 is more than adequate, but if you have the option for FW, you’ll notice the difference.

It all goes back to the very foundations of the technology. FW was designed to be an easier, more flexible replacement for early SCSI devices (high-throughput data transfer w/o having to assign device IDs, hotswappable, etc.); USB was a replacement for serial communications (input devices). Not even the same class.