This is all really interesting. I guess it's a good reminder, for me at least, that people's perspectives are often different. When my oldest son turned four, he had a party at our house (his first birthday party), for four of his friends, and all of the parents dropped off their kids, made sure I had phone numbers, and left. And that is absolutely what I expected them to do. He's a teenager now, and every party either kid has had or has been to has been drop-off. I think a couple of invites have noted that parents are "welcome" to stay, but I never interpreted that to mean, "Please do because we could use the help." I would never expect someone to ask if they can leave, but I probably would expect them to ask if they could stay. Honestly, it's never even occurred to me that some people have exactly the opposite perspective!
I feel like I've learned something!