Tokyo Skytree is part of the 'All-Japan Tower Association' franchise of 20 observation decks around Japan. One of the observation decks I went to in Fukuoka didn't have commercial or residential units, and appeared to be purely an observation deck and one sad little cafe.
Observation deck tickets in Japan are an order of magnitude cheaper than the observation decks in the states, which makes me curious how the economics work out. With notable exceptions such as the Space Needle which was built for the World Fair, most observation decks in the states are in skyscrapers that are developed with luxury real estate.
Maybe not coincidentally, Fukuoka tower was finished in 1989 in the midst of the Japan asset bubble, which succeeded a period of opulence and hedonism with the anticipation at the time that Japan would be the global superpower, until it didn't.