I'd consider it to be specifying the "maze" more accurately. The idea is to be able to come up with an interesting statement (such as "all mazes of this type ca

I'd consider it to be specifying the "maze" more accurately. The idea is to be able to come up with an interesting statement (such as "all mazes of this type can be made of just two pieces"), but if you include non-reachable areas as part of the maze, then it reduces the number of interesting statements available but also doesn't add to the process of examining the routes and solution. If you consider the same type of maze but have it in three dimensions, then all of them can be made out of just one piece, so it's clear that the definition of "maze" is too encompassing.