[Retric]

This is not exactly true, the magnetic fields on HDD migrate around on the disk over time and eventually become unreadable by the disk. In theory the data remains recoverable for significantly longer than that but it's not 'stable'. While historically not much of a problem it's a larger issue as HDD keep increasing in capacity.

HDD actually internally refresh data to avoid this issue so their much better as 'hot' storage. Tape is designed to avoid most of these issues and is much better for long term storage.

"Magnetic media – such as floppy disks and magnetic tapes – may experience data decay as bits lose their magnetic orientation. Periodic refreshing by rewriting the data can alleviate this problem. " http://en.wikipedia.org/wiki/Data_degradation