The easy—and correct—answer to that question is, "Some are, some aren't." Since once in awhile an argument hinges on whether or not some random detail in the HM is the result of pure geekiness, it's helpful to demonstrate that the phenomenon really is there. I think a good example can be seen in the attic scale model photos that we've referenced more than once already, comparing them to what is actually there.
As many of you know, they build a scale model of the whole attraction beforehand and photograph it to death, using this as a tool for interior design, finding unforeseen problems in presentation, fine-tuning arrangements of group figures, etc.
The photos are not generally intended for public consumption, although many do eventually get published in various Disney books and magazines. They're fun to look at, no doubt about it.
Anyway, it seems to me that the Imagineers who revamped the attic contents for the Constance overhaul in 2006 were Haunted Mansion geeks. They went back to the old scale model photos and incorporated details from them that the public could not possibly be expected ever to notice.
Let's take a look.
This 1969 shot of the Hatbox Ghost corner of the attic model has some curious props in it. There's an unusual red couch of some kind and some items suggesting the presence of a Victorian-era big game hunter: a water buffalo head and an elephant's foot umbrella holder.
Compare this scene with its counterpart in the scale model, and the global mystery is solved by another appeal to the geek factor. It turns out that the smaller globe is placed almost exactly where its miniature twin sits in the old photo. Someone might argue that this is a coincidence, but after the example of the big game hunter's red couch, I'm inclined to think it's deliberate. If the responsible parties ever happen to click on "Long-Forgotten" and read this post, all I can say is . . .