The dropdown has a few, important shops in it for quick access to particular pages; If I were to put every shop into the menu, it'd eventually get quite long.
Clicking "Shop" brings you to a "shopping mall" kind of thing; where you have access to every place that sells something on Windlyn. We bring up the Second Hand Shoppe first because it's the cheapo clothing store.
Hovering over "Shop" brings up shopping-related options. The two actual shops that show up in the dropdown are special-- the event shop and the special currency shop.
Once Upawn a Time isn't really a shop, because it doesn't sell things
to users; but it's shopping related, so it doesn't get to be in the carousel of the "shopping mall", as we called it earlier, but it still lives in the shop dropdown.