Do they swap it with a cheap model or just take it and run?
Note that this is based on mental estimations of a ten year old memory. I may be off about how small it was, but I think the estimation should be accurate in essence.
I also find the comment guests "guests will most likely attempt to take the mattress at night when the reception desk isn’t open" odd, since most four/five star hotels usually have a front desk that is staffed 24 hours.