Why three toilets:
The "half bathroom" is by the kitchen, living room, ect. It's just a sink and toilet. This is the one that, by courtesy, guests use. Because there's no bath, guests don't see our towels, toothbrushes, and other mess that accumulates. (No toothpaste stuck in the sink!) We also put prettier fixtures in there, because it's the one we go in most often.
Then there's a normal bathroom (toilet, sink, and tub) that the kids and overnight guests can use.
Then we have our master bathroom, attached to the master bedroom, which has a toilet, shower, and two sinks. (Useful when my wife and I brush our teeth at the same time.) The point of keeping it attached to the master bedroom is basically so we don't have to walk around the house in "bedclothes" when we have to go to the bathroom in the middle of the night.
Another thing that this article misses: A lot of people like to loose track of time reading on the toilet. There's nothing wrong with that when you have extra toilets in your house.