There is a concept in model railroading called “selective compression,” wherein you might model a few houses to represent an entire neighborhood, or a single factory to represent an entire industry. I think MMO devs do the same thing, with lesser or greater success. The sometimes drastic transitions in WoW (and I am sure other MMOs) reflects this desire to represent in a small space (even virtual space isn't unlimited) a wide variety of environments. I'd be interested to see exactly how big Azeroth really is in real space.
I had a big issue with one reviewer of STO who complained about the galactic map representation of Warp Space, because I thought it was one of the cleverer ways to represent getting "from here to there" right when I first saw it.
Overall, it is not at the edges of a game environment where you should judge its effectiveness, but the middle. Do you feel like you are in the middle of a strange planet, or a starbase, or a jungle, or a medieval town? Someday we'll actually have holodecks where you can truly immerse yourself in the game. But honestly, you don't really want a game world as big as the real one, because in the real galaxy there is a lot of "empty" where nothing is going on.