I believe the USB port may have some diagnostic use to DISH, but not to consumers. This is my speculation based on what I was told by DISH a while back. They wanted to borrow my 522 to download some logging/error data. Before coming out to my house, they mentioned that they might take the thing and leave a replacement, or they might download what they needed to a USB drive. Hmmm ... caught my interest. I offered to download to my USB flashdrive and then email data or burn a CD with the info for them (to save a trip) but was then told you need a special USB drive.
Take that FWIW. It may be erroneous, I may have misunderstood,, or there may be something to it. It could be similar to the phone connection to the 522. You can dial the phone number your 522 is connected to all day and it won't answer. UNLESS the incoming call is coming from DISH. I believe they use caller id to determine this. They might be using some similar technique with a custom USB driver that only recognizes "friendly" USB devices.
All this is just speculation on my part, based on their brief mention of USB in our phone conversation.