Picking an End Point for the Revolution

How is it, that the French and American Revolutions, so close in time and goals, had such different outcomes? One answer is that the American Revolution built on the foundation of English legislative traditions whereas the French had no such traditions (at the time of the revolution it had been 175 years since the last time the Estates General had been called). Which is to say the American Revolution modified the existing system, while the French Revolution was an attempt to completely replace the old system. This gave the American Revolution an obvious end point, which the French Revolution lacked.