The neat thing about using Photoshop is being able to work with layers. I don't know what other mapping software gives you that sort of flexibility in being able to layer things, such as having a different layer for cities, names, roads, waterways, etc.
And then if you really want, you can make the maps look all funky, like they were made on parchment or carved in stone. I haven't actually tried any of those options, but I don't think it'd be too hard to do.