Jeff is quite right. Object libraries can be on top or below but, we have shown them below because when you load a new RTMM scenery folder into FSX, FSX puts the folder on top by default. Since most of us load a lot more new scenery folders than we do object libraries, it just made more sense to keep the RTMM object libraries below the RTMM scenery folders. In that way, when you add a new RTMM scenery you can get right to flying with out having to move it in the library.
Rod