For hundreds mabye thousands of years tile was installed on concrete and concrete only. Here in New England we still have a lot of homes where the tile is laid upon concrete with wire nailed right to the wood studs,I tear them out all the time.In the 80's maybe earlier Durock(durable nailable concrete board reinforced with fiberglass for strength) came out and the job became much easier and more precise.You just nail or screw your durock to your floor or wall and boom Lay tile right down, a wondrous thing I used for about 15 years.But one time while in the tile store in Atlanta , I saw a new product Hardy board.
Now durock is great , but has one big weakness water gets through it its not a WATER BARRIER .Durock is not effected by water but it doesn't stop it either. Hardy board on the other hand is a actual barrier that stops ANY water penetration when properly sealed upon installation.Silicone II 50 year calk used to seal the hardy board joints will insure a waterproof installation and total protection of the wood wall studs underneath.Given the choice because both products cost the same I prefer to use hardy board in all my tile and marble installations, and most definitely in all wet areas.