I agree with everyone else that it's house rules and to each his own. Everyone is different. Let me ask you this? Do you see yourself going into someone's home and eating a huge meal, leaving your dishes on the table and walking away and not helping with the clean up? Some people wouldn't think twice about it but I myself could never do that. I feel that if my host/hostess were kind enough to do all cooking and preparing the least I can do it help with the clean up by, at the very least, cleaning up my dishes and putting them by the sink.
I'm just using this as an example because as adults we normally don't go into someone's house and play with their toys. I make my son help clean up wherever he plays even if it's just a few toys. I also ask the children that come to our house to play to help clean up. My son has to clean up his toys each night before he goes to bed so there are never toys laying around that the kids didn't pull out together. Cleaning up together helps kids work together as a team, to learn teamwork. It also helps them learn a sense of community and I believe that it will help them later in life when they go to work and need to work with a group to get a job done. At the end of the day would the boss at a construction site care whose scrap metal is lying around? No, of course not, he would just want it cleaned up.
Maybe you could have each child pick up a certain number of toys depending on how long they've played. If you don't care if the room is spotless then that would probably work. Another suggestion, label everything so kids know where stuff goes. Otherwise you'll find it in the wrong places. If you think about it, a child may say to you "but I didn't pull out any toys" but really if the child is playing with toys that are laying out on the floor he would have had to pull it out had it not been out. It's irrelevant, they played and now they need to help clean up. Teamwork.