nile:
You're confusing digital video data (good ol' computer bits & bytes) with video feeds/signals (color information for TVs/monitors).
What you're looking at is a video capture device that hooks up to a computer via USB 2.0. The description on that site is somewhat misleading. Traditionally, one would buy some kind of TV Tuner/vidcap add-in card, which would receive the cableTV/gameconsole/vcr/camcorder video feed and convert&combine that with the normal video feed that your graphics card would generate, allowing you to watch tv inside windows/mac environment. USB 2.0 comes into the picture as a means of connecting external devices -- transferring data, NOT video signals. That USB 2.0 (or Firewire) connection is required for devices like the eyeTV because it took the incoming video signal and encoded it as digital video data, which then gets sent to your computer thru the usb/firewire connection. Since high-quality video data takes up A LOT of space, a fast connection is needed by the eyeTV if you want to view the live video in real-time. More importantly, a fast connection is needed for copying the digital video to your harddrive. USB1.1 can barely keep up with 320x240 @ 30fps (depending on the codec), while USB2.0 and Firewire are sufficient for 720x480i @ 30fps (depending on the codec).
DV-format video (like from miniDV cameras) has a bandwidth of roughly 3-4MB/sec... requiring 1GB for just over 4min of video+audio. That's where the Firewire interface comes in -- it's dominantly used for transferring DV video.
"480p" (720x480p) has little to do with all that. Just as Strell said, we're expecting Rev to connect to TVs as well as computer *monitors*, not the computer itself -- simply using the monitor for displaying. So the Rev might use VGA boxes or DVI or component output, etc for monitor display. Those are the kinds of connections we need if we wish to view 480p video.
(viewing/capturing 480p video feeds within windows/mac is a whole different ballpark. There are no consumer-level devices that will capture 480p video -- you'd have to get broadcast industry hardware that sells for thousands of dollars)