I'm not saying you don't own the data, I'm saying it's more expensive than storing it yourself. Obviously it depends on the purpose and budget; if you need it to be highly available and secure, and you have thousands of dollars to direct to the project, the cloud is great. If you want to make a backup of all your DVDs that fits on a single disc, it might be overkill.

The sort of data suited to discs like this is probably pretty different than the sort of data suited to an S3 bucket. It could make a decent tertiary backup though, a local copy of your data stored on offline media can be a lifesaver.

This isn't a competing technology to the cloud, it's complimentary.