I have placed pups in all sorts of homes, from very large homes to those that arent so much so. I have also been to homes to collect dogs for rescue, (not just saints, but another giant breed) and i have to say that the most dogs put up for rehome have been in this case from the larger ones, where the dog has made a mess of their lovely landscaped garden! These dogs have often been confined to just one small room to save damage! Im not saying that all people with large homes/gardens are the same, but it does seem that the dog is more of a status symbol & a case of 'look what we have' kind of situation.
We personally do not take people on what they have or dont have, I dont care much for status, never have. All I am concerned with is can they look after, care for & love this puppy as much as I could? I find the meetings with them & watching the interaction with our other dogs, mum & pups tells me alot, as does my dogs reactions to them.
So for us, size of home, garden etc is irrelevant. I am very careful tho not to place where there are lots of stairs into or out of the property, that in itself is a problem for babies, let alone adults. But i do agree that the larger the garden, the more chance of the dog not getting the required socialisation at a young age, even adult hood to experience 'life' can often happen.