House rules apply even if you own the appartment. However, whereas a baby crying is certainly annoying for the neighbours, it is considered "acceptable noise" even in Switzerland, as this is not something the parents can avoid, even if they do their best. Which of course does not mean that the neighbours are not allowed to find it disturbing, they (or the landlord) just can't do anything about it. As some people have mentioned earlier, it is usually easier to share a house with people in similar stages of life and habits and therefore for a family with young kids, a house with other similar families is simply more suitable than say, a house with retired couples who really like their peace and quiet. So it's only reasonable from the point of view of the landlord to try and find a tenant who would fit in. I don't see why this was groan-worthy.