Good point, but if you look at the original mythology, the Greeks had very distinct "jobs" for each god, such as the goddess of the yellow that you see on the edges of clouds when the sun is behind them (Very long title, I know
). That's about as distinct a job as it gets.
So, Okeanos is the god of the ocean
, while Poseidon only has control of seas
. They are similar, but not quite the same thing.