Firstly, liturgical diversity is a richness of the Orthodox Church. It doesn't matter if I attend Liturgy in Poland, Serbia, if it's byzantine, Coptic or Armenian - I feel it's Orthodox, the basis is the same.
Secondly, the liturgical rite comes out from the theology, Liturgy illustrates the teaching of the Church. That's why Eastern Catholic Liturgy seems to be similar to the Orthodox one (and what Roman Catholics like to claim, especially if they see somebody who is interested in Eastern spirituality and they're afraid this person could convert into Orthodox Church), but in reality it is not. Latinizations, abbreviations, generally not maintained some traditions such as All-night vigil (or Vespers or Matins) etc. I know people who have attended Orthodox and Greek Catholic Liturgy; they were in agreement that they were different, in Greek Catholic church they felt almost like in Roman one. Sometimes I read also some forums of Polish Roman Catholic traditionalists. On the one hand, they appreciate byzantine Liturgy. But on the other hand, they would like to introduce such things as receiving Holy Communion in the kneeling position what's inappropriate in the Eastern Liturgy