Their difference is that hard bait can be used in a variety of swimming layers and suitable for the open waters, moreover, it can not only attract fish to attack by the mimicry, but use the sound to stimulate the fish to attack.
Topwater bait for basses includes many different types of bait in various shapes to achieve different action on the surface of the water. Like uplanders, poppers, buzzbaits, wakebaits, minnows and prop lure and so on.
In America alone, over 15 million people list saltwater fishing as one of their favorite recreational activities. To some extent, the word saltwater is inaccurate. Changing it to something better would make a lot of sense.