FireWire, uses a "Peer-to-Peer" architecture in which the peripherals are intelligent and can negotiate bus conflicts to determine which device can best control a data transfer
Hi-Speed USB 2.0 uses a "Master-Slave" architecture in which the computer handles all arbitration functions and dictates data flow to, from and between the attached peripherals (adding additional system overhead and resulting in slower data flow control)
so thats where ur cpu cycles go…
some firewire cams also deliver uncompressed frames without significant latency, unlike DV cams which are 1/2 second late
and of course go for non-interlaced
capture cards are ok, analog video cables can go up to 50 meters, but you get interlaced video on higher resolutions than 320x240
hope this helps