It's not easy to wrap tarsnap. If you own one tarsnap account, how do you split that up into multiple accounts? You'd end up writing code for account management and authorization (not written by colin).

Also, you can't provide the guarantees you want. You could hire 24 hour tech support but will they be able to troubleshoot colin's servers if they are down and he is sleeping?

Update: another business idea for Colin. Keep tarsnap as-is but license the server code for a fee so others can run a business as proposed.