I know what it does, and you are not going to be getting prices that you can afford from anything backing to S3. This (S3's storing everything so redundantly)

I know what it does, and you are not going to be getting prices that you can afford from anything backing to S3. This (S3's storing everything so redundantly) is what I see as the main benefit that tarsnap would get you, since the encryption itself is the easy part---just GPG your dump before writing to tape. Now, I might be strawmanning you. What does tarsnap get you in particular that tapes do not?