I believe the idea is that some doors/chests will already be opened/unlocked. I understand the concept though,

"If I'm not doing 100% why do I need to worry about if the chest is already open?" "If this dungeon has no moving/unlockable parts, than why not since it's identical either way?"

The idea is to keep the playing field level for everybody I suppose, and minimize the amount of "but what if..."s