"...if we can do an effective marketing job of convincing people that not only do they need that incremental storage, but they need to back it all up..."
Unlikely. People already *know* they should back up their data. They still don't. Even techies frequently don't back up their personal stuff. This is not a marketing issue; it's a user laziness issue. If it can be solved at all, it will be by default-enabling full backups and shipping machines with a second drive for the purpose. No offsite like that, but if you have need of offsite you probably have more to worry about than your MP3 and porn collections. Cloud backups are also a possibility, I suppose, but that still requires user effort, if only to figure out what needs to be stored. And that isn't going to happen. Ever.
From WD's perspective that works just as well, of course. They've no reason to care where backups go as long as it's on their drives. But It's not a matter of improving the message. The message has long been delivered. It's the idea -- specifically the idea that users will in any way take responsibility for their own stuff -- that's broken.