I would suggest that having the USB on the back seems like a very logical choice. It seems to me that it will really only ever get used in two instances:

1. To upgrade in the future. How often is this likely to be done? My money is on "not very" so once in a great while getting to the back of the unit shouldn't be a big deal for a cleaner front.

2. As an audio slave device to a PC. If you're using it in this fashion, most likely you'll have a permanent connection hooked up to that USB port. Do you really want a USB cable forever hanging off the front of your unit? I wouldn't.

If there is some other application I'm overlooking that would require you frequently plug in and remove a cable which would demand front panel access, please share. I can't think of any but would be curious to learn about something new. But as Iggy points out, USB extension cables are cheap and easy to come by. Run one around the side of your unit and now you have front access.