The U of Fl department of veterinary medicine (they do a ton of work with fish) says that salt works fine in treating ich either at higher concentrations as a dip, or lower as a long-term treatment.
http://edis.ifas.ufl.edu/FA006
My own experience is that heat really helps the most against ich, but salt helps things along as well.
Another thing to think about when comparing experiences is that there are different strains of freshwater ich, some of them more heat and salt resistant than others.
windsurfer