Yes, this is all true I think. Last year my friends and I stayed at the Marriott (wonderful hotel in my opinion, just hated the crowds of people) We originally had 5 people staying in one room. I know its room stuffing, but at least it was only one over. Then last minute a friend invited two other people to stay with us.
And anyone who's been at the Marriott knows the rooms aren't exactly huge, 5 people would have been tight enough with our luggage. So besides the safety issues and using more supplies for the room then usual (which we all tried very hard not to do, brought paper cups and used bath towels that we brought from home), its just down right uncomfterable being stuffed in a room with 7 people, one shower, and limited sleeping/moving space. And never having a quiet moment to yourself after being in a loud crowded con all day.
I don't know about anyone else, but I enjoy my alone time to cool down after a hectic day.
So yeah, besides it being a legal issue with the hotel. I'd discourage room stuffing for the comfert factor, even if your not planning on being in the room for more then sleeping and bathing.