I think the customer should be very careful to read any TOS he is presented with before he pays for a service, and if that particular hosts TOS stipulates that they will not take back ups, nor be responsible for any data loss that may occur then the customer should absorb this and consider it when making the final purchase etc ...
By extension though I've often felt that hosts should have their full TOS, and a page of say 10 1 line bullet points putting across the most salient facts in non legal lingo as well (some hosts do this already of course), because lets face it, maybe 1 in 20 customers actually looks through an often VERY large and confusing TOS ... if that.
If a host does lose data, then obviously they have failed to provide the service they sold the customer, and should give a full refund for that particular term (monthly, quarterly or whatever). Any further compensation they give should be seen less as a duty, and more as a way to appease a customer whose data has been lost / affected.
As for financial recouperation - its a really difficult one and I dont know quite how to play it to be honest. For instance, who makes a judgement upon the value of data lost - neither the customer or the host are particularly suitable in this case as inflation/deflation of the theoretical value can happen all over the place . Perhaps some hosts should try an insurance scheme, where the customer pays a little extra each month, in the knowledge that if an issue isnt resolved to hist satisfaction, he can claim a certain amount of money (agreed upon before by host and customer) back.
This could be legally difficult though, and I really have no idea how you would overcome that.