SarcasmMode "I don't think it should be a regular occurrence italian as I say - but as a treat it's nice."
On holidays, camping etc it is sometimes impossible not to share spaces. My dd would hate sharing with her brother, he is half her age, he wriggles and talks in his sleep, no treat for her! 
Sharing a bedroom, or bed, being a normal occurrence for children, may lead one/them to feel that that is what the parents want. If anything untoward happens at least one child may feel it is OK because parents have allowed them to a shared room/bed.
I don't think this problems with this is common, but to be honest I don't have any idea how common it is.
I do know that a few decades ago most people had no idea what happened in so many places, in terms of abuse, now we all know and tr to behave appropriately but years ago we never knew.
"I don't want want a male child to automatically be presumed to be sexual when a female child not." I don't think I was doing that, I would be 'arguing' for privacy for both sexes. I would be concerned for a younger or more easily influenced child, I would not blindly assume any activity was down to the boy.
But girls and women are socialised to accept things in life, to play nice, not to challenge, to feel flattered when their bodies are discussed, or at the very least not to complain about it. I fucking hate it, but it does happen.
"Don't get me wrong I understand you - but it just feels such a shame that it can't be innocent."
Life with children can be innocent, totally! Rough and tumble and play, fun and games, jokes and japes! Just not naked, or inappropriateness, or inappropriately dressed, not sexualised and ideally (in my book) not in the same bed or same room on a regular basis after a certain age. Teaching children privacy doesn't mean they lose their innocence, if anything it may mean they can retain it longer, IMHO.
My ds insists on getting changed with me out of the room, but then lies in the bath naked with me chatting to him! They are working it out for themselves, he is 6. I would not want any child to feel ashamed about their body etc. But I just think when a reputable charity like NSPCC gives guidance then ordinary people should take note.
Lots of posters last night when almost laughing at this advice and claiming it was hysterics!