Just one one bedroom with oak trim vs pine/birch? Why is this?

I've seen this several times - maybe it's an Ohio thing, but either way I'm beginning to think there was a reason for it. In several century homes I've owned or viewed over the years - typically in a colonial, but my current Craftsman home has it too - there is always one bedroom that is "not like the others". All the bedrooms (upstairs, of course) will be trimmed in pine or birch, but one of them will be trimmed all in oak. And most, if not all of these oak rooms, also happens to be the only "bedroom" without a closet. It's also never the biggest room, usually one of the smaller ones. Anyone else see this? Any idea why this is? Or am I seeing patterns where they don't exist?