You don't even need the high-speed backbone. You could backup the files to a local drive. The latency might be bad, but trucks still have higher bandwidth then the internet.
True absolutely. But there's something more appealing to me about handing a drive across a counter, knowing it will be backed up in a few hours (assuming that is practical), and ready for me to be confirmed back home via my higher-download-speed broadband; rather than have the drive rattle across the country in a truck, sit in a mail room, and finally get processed X days/weeks later...
So Mall Backup Co takes two copies immediately. One on their local node and one that gets shipped back to base.
As soon as you get home you can access your backup (transparently) from the mall node. Then when the drive gets back to base it does another verification run and instructs the node that it can re-use that space.
It could be feasible in the UK; we can do same-day courier across the country, although I suspect it'd be expensive at low volume. Next day post gets there the next day pretty much every time, though.
http://what-if.xkcd.com/31/