@Ben Edwards
It's unlikely that any service would offer a free re-download, as there's still the cost to supply the things you've bought in terms of bandwidth etc, plus allowing multiple downloads offers up the opportunity to share account details around and let different people use the same download options.
Thinking about it though, it's not like you'd walk into HMV and expect them to give you a new copy of Boyzone if you lost your old one, so there's little difference between digital media and the hard version.
The motto here, as I'm sure you're aware, is keep backups of any data you can't easily replace :)