xkcd used 'Electra' as one of the list items, which could ether be one of the seven sisters of the Pleiades or one of Sophocles' seven plays. I included both lists for your enjoyment.
I've seen several groups listed under "modern seas" or "seven seas". One includes the north and south Atlantic, north and south Pacific, and others. Another includes the Aegean, North, Arabian, Irish, etc.
Yes, I think we humans are both fascinated with the number 7 and sentimental enough to want to 'recreate' lists that existed in antiquity, and so we try to force the world into that list of 7, even though the reality isn't so straightforward. Same thing happens with the 7 wonders of the modern world. Much disagreement on what should be included.