Earlier quoted context omitted.
"you're responsible for doing all your own offsite backups" That's going to be true no matter which cloud provider you choose. Their ToS almost certainly include terms which allow them to kick you off and refund any monies for any reason whatsoever. Good luck if you bought into their entire ecosystem and can't move elsewhere on a whim.
That's going to be true no matter which cloud provider you choose My company provides services to fortune 100 companies, and we host literally petabytes of data on their behalf in Amazon S3, but we don't have offsite backups. We (and they) rely on Amazon's durability promise. We do offer the option of replicating their data to another cloud provider, but few customers use that service -- few companies want to pay ove…
Reasoning: Your contract with Amazon promises durability and I'm sure there's a service level agreement with penalty/liability clauses. By implementing a redundant backup, you're replicating something that you don't legally need to have, double-or-more due diligence on the offsite backup security/credentials, and in case of a failure of Amazon create a grey area with clients "Do you have the data, or do you not?"
In short, there could be a very good business reason not to do offsite backups.