Um, no, it's not "different calenders" that makes for a different date between the Orthodox Christians and the Roman Catholics.
As in the early church AND now the Orthodox Christians (Eastern) the moon situation must happen + Seder has to happen=Pascha date.
Christ is the New Convenant, the New Testament. Holding Easter/Pascha before Seder has happened just doesn't make sense in the New Testament sense. Christ was killed after the Seder, to hold Easter before Seder happens, well, it just doesn't fit biblically.
ok, so yes, I think the fact that we use the julian calender for Easter determination of course will effect the difference between RCC and EO, so factor that into the equation above.