"Are people saying that they don't communicate with the bf or gf's parents? That is really weird. Why wouldn't you?"
I met DD's boyfriend's mother for the first time last weekend. They have been going out with each other for nearly 6 months.
It isn't weird at all to not communicate with your children's friends or partner’s parents once they are teenagers. IMO it sounds rather controlling to be in contact with the parents unless they are planning something major like going away to London for the weekend.
“I agree, speaking to parents is what you do if your kids are underage, or we are discussing primary school play date arrangements!”
This ^^
Why would I need to talk to DD's friends parents? DD complains that when I pick her up from a sleepover that I am the only parent who comes to the house. All the others text their offspring that they are outside. In my case it is because DD always has her phone on silent, and in one parent's case I am actually quite friendly with her so we just have a 5 minute gossip.
By the time I was 16 my parents didn't know the parents of any of my friends, and they certainly didn't know any of my boyfriend’s parents.
Back to the original question. Of course I let DD and her boyfriend go up to DD's room. I can't expect them to sit chastely in the living room being forced to watch something OH and I want to see on TV.
“We have allowed all partners in their rooms in the same way we always allowed friends in their rooms. This means they know we can go in at any time, as we would with friends - but we do a lot of loud approach steps and coughing and slow rattling of the door handle to give them warning we're entering!”
This^^ is what I do as well 
They keep the bedroom door ajar and I know they don't just sit and hold hands, but they also know that I can come into the room unexpectedly (I knock first).
You need to be able to give your daughter some privacy. She is 16 not 12.