>>37434333ahem
SO you see Lugia ok, LUGIA... Lugia is a DIVING. Yes. DIVING pokemon.
It doesn't originate FROM the ocean, nor is it a water based creature. It simply CAN dwell in the ocean and does so due to leaving its nesting place. Nothing about lugia actually suggests it should be a water type desu, more that it can utilize the water due to its absolute potential as a stronger pokemon. From a design perspective I can understand why people associate it as a water type. Sleek skin, orca-like components etc. But if you look at it from a different angle, it's more like a bird crossed with some sort of reptile.
ANYWAYS, the real question should be why it isn't dragon/flying or dragon/psychic. But flying will typically be prevalent as a typing if something has wings.