Personally, I think that Disney decided to pick rooms that were less popular at POR and CBR and added theming in an effort to make them more desirable. If you look at a map of POR, Parterre Place and Oak Manor are two buildings that are a little bit off from the main areas of the resort, like the pool and food court. The regular rooms have a lower price ands are closest to the first bus top, Preferred rooms are close to everything, Magnolia Manor and Acadia are fairly well located, near the second bus stop and are lower priced. RR have extra theming. (Similarly, If you go to CBR, the pirate rooms are the most distant, undesirable location (IMO) but have the extra theming and cost more.)
Basically, wherever you stay in POR you can at least say that there is some advantage to your room's location.
RR's are very nicely themed, but I'm not sure that they are really worth the extra $$. The rooms are the same size as all the others and offer few advantages other than theming. The other rooms at the resort are also very nice, though. The preferred rooms in AB are my first choice because they just are so close to almost everything, have really cute rustic theming and are set in lovely grounds. You can walk to the first bus stop from them if you so desire, the first bus stop is not all that far from building. 18 or 27 (preferred buildings). Some of the further rooms in Parterre place (RR's) are just about as far from any bus stop, as those are from the west depot (first stop).
I also agree that the bus runs around the stops in the order that it does so that it functions to bring those from the most distant rooms around to the main area (for dining, boat to DS, etc). Of course it only works as an internal bus in one direction.
All that is just my conjecture/opinion, of course.
All that said, I love POR and have happily stayed in multiple areas of the resort. FWIW, my room preferences, in order, are as follows:
1. preferred rooms in AB (most convenient)
2. regular rooms in mansions (combination of lowest price and good location)
3. Royal rooms (nice theming and good location)
4. regular AB rooms (good value, quaint setting)