This doesn't seem to be quite the same effect as the entire body of the slinky is not contracting. So, it isn't just that the bottom and top are moving together as fast as the entire slinky is falling, causing the bottom to remain stationary, but that the entire bottom of the slinky is remaining stationary (not just slowed down, but exactly stationary), in its stretched state, until the top of the slinky reaches that point. I don't think you are giving the phenomenon enough credit.
