I will agree with Chris in that a home with one bath (unless it is a condo/townhouse with one bedroom, etc) will not only be difficult when you have a large family, but will be difficult on resale as well. An older home may have fewer number of baths and if you notice, the rooms themselves tend to be smaller as well. What buyers were going after in say the 1960's, is a lot different than today. Buyers today want bigger rooms and bathrooms. Most areas of the country are this way, so I don't think the number of baths is a regional thing, per se.
So, having only one bath in a house could take value from the home and also make it difficult to sell, however it also depends on what you are comparing that particular home to. Do other homes in the neighborhood typically have one or 1.5 baths? Is one bath more the standard for that neighborhood? Perhaps the house is older and one to 1.5 baths is more common place. On the other hand, if the majority of homes have two baths and beyond, and you have a one bath, unfortunately you are the odd one out and nobody wants to be that person. Especially when you are selling real estate.
Hope this was helpful.
A lot of my buyer clients request 1.5+ bath homes so I would say that homes with only 1 bath will definitely be harder to sell if other similar homes with more than one bath room are available even at a slightly higher asking price. Also, when I have listed homes with only one bathroom, it is a very common feedback to receive displeasure in only having one bath room.