Typically (at Disney World) you won't ever be assigned one of those rooms unless the room you were originally assigned to was taken "out of service" for a maintenance issue that couldn't be resolved quickly enough, and that was the last available room (and that room had not been specifically booked). A more rare scenario is when a previous Guest does not vacate for some reason. And while I don't believe that Disney oversells, their policy is to never (knowingly) book someone who doesn't need/want that room type into an HA room; they are reserved for people who book them specifically.
WDW (and DL) have a policy that (as we understand it over on the DISabilties board) that type of accommodation must specifically be requested. Meaning, they don't just rent rooms willy-nilly, and then hope they can shuffle things around when I show up and require a HARIS room. Any of the rooms listed as "Accessible" on the website, and in their central res system must be booked deliberately - that way, someone who is hearing-impaired, and books a room with those features knows for sure that when they arrive, they will have that room type guaranteed.
In fact, it's one of the few "guaranteed" things about booking a hotel at WDW; everything else is pretty much a "request"!
So, if you ever find yourself in one of those rooms (and believe me, I wish I didn't *have* to - it makes travel so much more difficult because there are so few of them, especially at WL) know that it's most likely because your "regular" room had a problem of some sort, and to make sure you had a place to stay, they put you into an empty HA room.
Disney is pretty good about accommodating people in all situations - I know you probably wanted to be at our beautiful WL, and not anywhere else, but they might have been able to move you to your reserved room type at another Disney Resort hotel, or perhaps offered you a HA room that had a more traditional bathroom layout. Just always go down to the Front Desk for those conversations; since we know that all calls from the room phone to the "Front Desk" go to a central call center, it stands to reason that you will have a better chance at a successful resolution if you talk directly to the on-duty manager at the property.
I hope the rest of your time at WL was great - I know that people sometimes think that the HA rooms are bigger or somehow better, but they are exactly the same size, just typically with a different bathroom layout, and (at the refurbed hotels) lower beds that are "transfer height" for wheelchair/mobility users, instead of the new higher platform beds that you can store luggage under.
