Outboards are self draining, provided the drains are not clogged. The drains that clog are usually little holes in the lower unit. When you store the engine, once you are done the winterizing, have the engine vertical, disconnect the spark plug wires and ground them, then slowly pull the starter rope a few times, that will ensure the water pump is drained.
The Antifreeze thing is a new fad for inboard engines. I guess it the draining of the block is uncertain, then using this stuff would be an insurance policy to reduce the chance of a cracked block