I don't have figures on hand but what I can tell you is this. Every time a new technology comes out, it is generally backwards compatible. That means that as long as you continually move your files to the latest storage, you'll be OK.
Not to mention, when you are storing digitally, you have the option of keeping good backups. The backup means that should one copy degrade or become damaged, you have a spare. So long as you check on the files to make sure the storage is working, and keep it safely stored, I think you'll be OK.