
It may not actually be their fault, though
If I remember correctly, there was a lawsuit a while back that may be related to this... a guy was leaving a company and asked his manager if he could use him as a reference, the manager said "ok" -- then proceeded to trash talk the guy to anyone who called.
The guy sued the manager, which I can understand, but he also sued the company... and if I remember correctly, he won. Which seems a bit unfair, but I reckon if I was being smeared by my former manager I wouldn't be thinking too clearly either.
At any rate, if a company can be SUED for something that one of their employees says of their own volition... then it makes for them to start forbidding the practice of giving professional references.
"We are all born originals -- why is it so many of us die copies?"
- Edward Young