Porcelain Bathtubs, for the most part, have not changed very much over the years and are usually found in older homes. The biggest change over the years in porcelain bathtubs has been the size of the tub.
The older bathtubs are much deeper, and are ideal for soaking. "They don't make ‘em like they used to" is a saying that is heard often, and is the reason that homeowners decide to keep the older tub and refinish it to bring back the shine.
There are really only a few different types of bathtubs that are found in the bathrooms of homes today. Older homes usually have recessed Porcelain Bathtubs, perhaps in a different style than what is pictured, or Claw Footed Tubs. Newer homes generally have lower cost, easier to install, one piece Fiberglass Tub/Shower or Walk-in Showers instead of porcelain tubs.