Interesting. I wonder why they want that? If the employees are acting as an extension of the company you would think that what goes for the office, goes outside the office as well. Maybe suggest that employees have separate handles (user accounts). One for personal use, and one for work use?
That wouldn't really work for Facebook - but then again... should the company always expect employees on Facebook to follow corporate suit?
Let's put it this way, the corporate world is getting nuttier and nuttier every day. A few years ago I worked of a major financial institution, one of the oldest in the US. Everyone in the company had to go through sexual harrasment training. During the class the instructor posed the following scenario...
You are on your vacation and you are in a restaurant in your neighborhood which is 50 miles from your office. Unknown to you, one of your male employees is in the bar telling dirty jokes. Unknown to either of you, one of your female employees is also in the bar and she overhears the joke. She spots you and comes over to tell you the your male employee, her co-worker, is telling dirty jokes in the bar and they are offensive to her and she feels this is sexual harrassement. She asks you to go into the bar and reprimand the male employee. (Keep in mind, everyone is off work when this is happening). The question was, are you responsible as their boss to say something to the male employee?
Now everyone in the class figured this is too bizarre of a circumstance and the answer had to be no, you are not responsible. Well, according to the bank not only are you responsible to say something but also to give the employee an official verbal warning the next time everyone was in the office.
So, as you can see from this sad, insane and totally true story, some companies believe that if you work for them then you work for them 24/7/365 and they have the right to dictate your behavior to you.