i dont think the 'coming out' is so much about people revealing their sex lives,more that they dont have to hide anymore because often it can be very difficult.
its very easy to have agreements for D/s couples in place such as not to use the term Master/Mistress,not always sit at their feet etc and all the little probably unnoticable to us everyday things but its very easy to slip up.
'vanillas' sometimes notice and can get the wrong idea,so sometimes it can be a honesty is the best policy type situation.

and if people are happy and dont want to hide then why should they.
ive learned to my cost that most people dont understand and react badly but then when thats the case apart from making life hell for a while they're simply not who you think they are and not worth the time of day.