Clearly the legendary from Y looks a lot better than the legendary from X.
I don't disagree, but I think it has to do with the order in which the games are generally listed. You see it all the time- the HeartGold board, the Black board, the Black 2 board... The first listed version gets the more popular board. You never hear it said "Pokémon SoulSilver and HeartGold", or "Pokémon Pearl and Diamond", or "Pokémon Y and X".