Wrong! Quality is important; however, I thought it was a standard rule that you should never use flat paint in a bathroom because 1) it's porous; and 2) the damage that can slowly occur due to the penetration of moisture. Even with a fan and/or window, flat paint in a bathroom is like a sponge, and where do you think that moisture is gonna go when it's absorbed? Due to the heat from steam/warm water temps, it can lead to the growth of mold/mildew in places you won't see until it's damage warrants full replacement of drywall, studs, flooring, etc.
Unless something has changed in the wonderful world of paint, I thought a minimum of semi-gloss was recommended for rooms with high moisture unless some sort of barrier or water-resistant primer was used underneath.