Too bad they didn't say which drive, company, or model they used.
You can also find that article here.
http://www.pcworld.com/article/2062254/25-000-drive-study-shines-a-light-on-how-long-hard-drives-actually-last.html
But this does show us why backing up your data is so important.
On a secondary note, it also highlights the importance of using RAID 1 (redundancy) as a means of helping to protect your data from faulty disks.
However, there's no substitute for backups. You may end up with corrupt data due to a sudden shutdown (blackout, blue screen of death in the middle of an OS update, blue screen in the middle of resizing your partition, etc), corrupted data due to a memory error when writing to the disk, a virus corrupted a file, your HDD was taken hostage by a virus that encrypted all your data with a key that's kept online, etc.
So even though this says that an HDD may still be running more than 80% of the time over the course of 4 years, backing up critical data is still essential. And, once we consider that most of our essential files can be stored on less than 32GB of data (well, most people - not content creators, business execs, etc), we don't really need anything more than a few flash drives, a small home NAS, and/or some cloud storage to backup our data.
=)