So, I'm sure this has been asked before, but in the Elder Scrolls IV: Oblivion we visit "Oblivion" and are left to assume it is the Deadlands. However, we also supposedly visit Boethia's realm as well as Peryite's realm. Both of these realms, however, look exactly the same as the Deadlands! Am I missing something, is it a gameplay mechanic, or is there a lore-related reason for this? Thanks!

I credit it up to gameplay mechanic, and explain it by saying that Peryite and Boethia happen to have lava-y parts to their realms too, and those parts are the ones we just happened to see.

Gameplay mechanic. It makes for a nice handwave whenever you run into something you don't like. This is especially true for aesthetics. Visuals aren't really as important if you can replace them in your mind with what you'd prefer to see.