Dish soap is good for cleaning dishes which are not porous and can be rinsed thoroughly. Granite, Marble and Grout are all porous which means oils get trapped in the pores and must be lifted out.
The problem is that dish soap when used on countertops will leave a residue. Even after rinsing with a rag or sponge several times has been found to still leave a residue. Even if not noticeable with each application, over time it builds up like soap scum in a shower to the point that the countertop begins to look dull and may even become stained from the residue build up.