Unfortunately Lone_Ranger it isn't as simple as you suggest.
My experience of any crew working together and this is the same surely for any unit of staff who work in a 'team' environment, generally chat with each other to bond. This actually dare I suggest is everyday CRM at play.
So when you, as I am sure you must have, asked a colleague whether they have a partner, or anything to do with potentially personal life interests - it can sometimes put that person on the spot. Without the questioner realising it. Even down to the questioner refering to 'she' about a partner they assume the other person has. Yes we all try to tow the politically correct line of never labelling someone as a he or she but we all make mistakes. I have.
So without realising it we all can cause some of our gay colleagues awkward moments. So you may find that these colleagues that make their orientation overt is simply them firstly trying to be honest with you and anyone they work with and secondly to avoid both parties ending up in a awkward moment when one party realises what they may or may perceive to have said, that may have caused offence or a perceived offence.
Some like to bottle it up and continue to lie to your face to avoid embarassment, others will be honest with you. This I feel should be embraced and respected if that is how they deal with it. We are all different.
I agree we do not need to know what goes on behind closed doors - unless you ask, but frankly to me everyday conversation lend themselves to subconciously probing into the other persons personal life.