When they say gold prospecting, they mean looking for natural gold nuggets in the mountains and in streams. Most gold nuggets are tiny, so you need a machine that is sensitive to tiny gold, which is why most people use the Gold Bug 2, Whites GMT, or a Minelab PI.
As mentioned, beach hunting is different, you are not looking for tiny little pieces of gold at the beach, you are looking for rings, big chains, big earrings, etc. The hardest part of finding a beach hunting machine is finding a machine that can handle dealing with the saltwater, which most machines can't do. The proven beach machines are Minelab BBS/FBS machines, Fisher CZ machines, Whites DFX/V3i, or a PI. The waterproof VLF machines are the Excalibur 2, Fisher CZ21, or Whites Beach Hunter.
Most guys use the Excalibur for beach hunting, second most popular is the CZ21, Beach Hunter isn't used by many people.