Well, ..., you are very right in thinking that the Full Moon occurs at different times wrt to Earth time zones. It just so happens that todays Full moon (07-Feb-2012) occurs just before moon rise in the EST time zone at 16:53:53 (~4:54PM) and coincides roughly with Moonrise. However, It occurs at other times over the course of the year and very rarely at Moon Rise. Now-a-days It has more to do with when the lunar disk achieves 100% illumination rather than when people perceive it as being full.