Beyond that, unrestrained encryption is dangerous to corporations, because what's to stop a ticked off employee from encrypting everything in the office
What to stop him/her from shredding everything in the office? This is a personnel/legal problem; there's nothing special about the use of cryptography (except that it might be reversable).
Reversability is the main difference - the disgruntled fired ex-sysadmin can encrypt everything and promise to restore it for big bucks plus amnesty. On the other hand, hiding the backup tapes and shredding everything is relatively reversable as well, and has the advantage that you can threaten to sell it to the competitors, so it's not much different. When I was an undergrad, an ex-sysadmin left the University, and a week or so after he was gone, the database system announced that it would self-destruct in a week. They had to keep the system shut down for a couple of weeks and change the system clock while they hunted for the time-bomb, and the same sort of thing could be done in many modern systems without crypto, though crypto makes it easier.