No I think it's made up, there is no policy, and the lawyers couldn't care less, it's just something people do to massage their own ego.
It is absolutely not made up, and yes, some companies absolutely do care.
Nope. I previously worked at a very big tech company (not Google) and they definitely had guidance like that in the social media policy.
I can tell you firsthand, it's not made up. Wait, did I just brag in your opinion?