This is actually true with many online booking systems, especially the ones people actually use. I've been told this using at least 10 different booking sites at over 20 hotels since 2005. At one major chain in downtown Cincinnati the clerk brought the manager over, who looked at the rate, and proceeded to pick up the phone and contact corporate to adjust the rate up, they manager told me they were losing money at that rate.
Turning over a room (to make it habitable for a next guest) costs wages, and that's just the bare minimum cost that I can think of. There are probably a dozen hidden costs associated with allowing someone to stay in a room.
