Answer to the first part of the question is as follows, courtesy - Answers.com: . "Satellites of satellites No moons of moons (natural satellites that orbit the natural satellite of another body) are known. In most cases, the tidal effects of the primary would make such a system unstable. However, calculations performed after the recent detection [4] of a possible ring system around Saturn's moon Rhea indicate that Rhean orbits would be stable. Furthermore, the suspected rings are thought to be narrow,[5] a phenomenon normally associated with shepherd moons." http://www.answers.com/topic/natural-satellite#Satellites_of_satellites . For the second part of the question, my web search did not yield any answer. But it has something to do with the gravitational pull of the planet to which the moon belongs and the gravitational pull of the moon itself. Natural satellites, unlike man made satellites, do not have the benefit of propulsion to resist the gravity of the major planet. Even manmade satellites that orbit our Earth's moon will drift away into space or crash onto the Earth or Moon once their Solar Panel charged batteries run down completely or when their rocket propulsion fuel is exhausted.

As of 2009 there are 180 moons with moons titled and catolouged under asteroid moons and the moons of minor planets