Jupiter, Saturn, Uranus and Neptune all have rings. The overlap between "gas giants" and "rings" is 100%, based on our data. Jupiter's are the least impressive but Jupiter is also closest to the asteroid belt so there was probably some orbital hanky-panky early on that proscribed many rings for Jupiter. Earth's moon is kind of obnoxiously large, all things considered. This is probably due to a cataclysmic impact early on during planetary formation. It certainly perturbs our orbital mechanics out of what we see elsewhere. Neither Venus nor Mars have moons (really - Mars has a couple captive asteroids) while Earth's moon is huge - there are only four in the solar system larger (and one of them is larger than Mercury). Anyway, our huge moon basically precludes us having rings... because we had them when the moon was forming.