Tarsnap to encrypted backup is what dropbox to file syncing (to a certain extent, obviously). I can understand why for someone knowledgeable like you, the benefit isn't obvious, just like we don't see the benefit of dropbox over other tools. But certain demographics will see tarsnap/ dropbox as value added, and is willing to pay for them (with good reason, too).
I know a lot of developers who have never spin up an EC2 instance, can't get their way around setting up a server, and certainly is not interested in maintaining an offsite server for backup. To them, tarsnap with its command line provide enough simplicity to be used (of course, it can be much better, as patio11 and alot of people pointed out).
