It's interesting that you should mention banks. Banks routinely go under, and in almost all cases your deposits are only 'safe' up to a certain amount. Most data stores are worth well in excess of that amount, so if you could not reasonably expect a bank to hold on to a very large amount of data it stands to reason that you should not trust some service provider with data that has serious value without a secondary system in place.

After all, their liability will almost certainly be less than the value of your data, in which case there are two reasons to keep extra copies, both business continuity reasons and direct economic ones.