Hello,
Actually, this practice is becoming more and more common. I am pursuing an Executive MBA and have more than 15 years work experience. I currently work for a Fortune 500 company that has this same policy.
You may be surprised to also learn that this protects you as an individual and your reputation.
We recently had an employee who left the company and sent a flurry of reference requests through LinkedIn, etc.
Many people recommended this person based upon their working relationship. However, what these people did not know (because HR could not discuss) was that this employee was asked to resign due to criminal activity. I am sure most colleagues would not have recommended this person had they known this. But since they ignored HR policy they are now, unfortunately, associated with this person.
I think most reputable companies will start instituting similar policies.