Well, the type of parent I am of course I would ask. It goes both ways though, if you're going to have someone's children in your home full disclosure is part of the deal. Are you saying that when you have other children in your home you don't feel obligated to let the other parents know the agenda? Yep, my job to ask but it's your job to tell. It goes both ways, when you have someone elses kids under your supervision you take on their safety. There should be no mis-communication on the front IMHO. I'd much prefer a mutual respect for each others parenting style. I'll agree to disagree with you but I can't imagine letting my kid hang out where the parents don't feel they need to let me in on what's happening.
When dd13 goes over her friends' homes, she makes the plans - I never speak to the parents. Her bff's mom is a good friend of mine, so we talk about things when we see each other, but do not call each other regarding specific plans. If I care to know if boys are going to be there, I'll ask my dd. If she lies, she's in big trouble (and her bff is the type of kid who tells her mother EVERYTHING).
Sometimes dd13 wants to invite her friends over, and I'll have to leave the house during that time. I let her know to tell her friends to tell their parents that they will be alone for a little while.