I think the difference in my mind is that the variances in Greek mythology are organic. The differences in Irish-specific mythology are the result of waves of invaders trying to suppress them and portray their culture as inferior. First the Romans, and then the Catholic Church. The Greek myths were, yes, amalgamated into the Roman empire in much the same way, except with the Greeks, they already had the tendency to record their own histories and were therefore able to preserve a version of their past for themselves. And, as far as the Catholic church goes, retelling of their traditions was never outlawed in the same way since the Helenistic civilization was not only closely tied to the Romans - with which Jesus himself had direct history - but had largely faded by the time the Catholic church came to power. In the case of Celtic mythology, however, it was a tradition that was still alive and well when the Catholic church came to their shores and the people were put to death en masse if they defied the orders of the church in reciting the "barbaric, heretical" version of events instead of the version that the church favoured.<br/><br/>This didn't happen on the same scale with the Greeks because they were considered civilized and enlightened.<br/><br/>It's the same bone I have to pick with how colonization of the western "new world" eroded native culture in very strong ways, imposing Christian themes and values on already-standing oral traditions. Because it wasn't recorded in a "civilized" manner, it was considered disposable. As with the Irish and Scottish in particular, there is no known record of any original tales without the Catholic and later European influence.