I think the premise of the original question might not be accurate. The premise seems to be that disney has a mistaken view of how full the resorts are, and this is causing fewer discounts.
I don't think this is true at all. I think WDW has extremely sophisticated models for understanding exactly how full the resorts are and will be. I don't think they are in the business of being tricked. I think their historical data is extremely reliable and they have a very strong sense of exactly what is going on.
The calculation whether to offer a discount is a complicated one, but the core principles are straightforward. You figure out the extra overhead that each additional room adds to your costs. You also make a prediction whether you are going to fill up at non-discounted rates, using all the tools at your disposal. If you are going to have empty rooms, you'd generally sell those rooms for more than the extra overhead involved in having guests in these rooms.
There are two other principles at work: (1) other than through very limited channels, you can't go too low on price because you undercut your ability to sell non-discounted rooms in the future by lowering expectations, and (2) you also need to factor in the additional overall revenue that will be recognized by getting additional people in the door.
These things are cyclical, and my hunch -- and it's only a hunch -- is that WDW is in a state of very significant transition right now. I believe that it is taking a short term revenue loss on rooms right now -- that is, it is not offering discounts even though it knows that it could enhance revenue by doing so. For example, I think there are a number of rooms for the next several months that will go unused that could easily be filled by offering a discount. I think WDW is at sufficient capacity that the added overhead of filling these rooms would be exceeded by the room revenue plus the additional spending revenue. So why aren't they offering more codes?
I think the answer is that disney is exceptional at canibalizing the good ideas of other theme parks. Universal's FOTL really turned some heads, and I think the next decade or so at WDW is going to be significantly marked by an era of on-site guests receiving considerably greater perks than off-site guests. I also think you're going to start seeing class-related perks -- that is, guests spending more on accomodation are going to get greater perks. You're already seeing it with the 10-day extra window for dining reservations, and it's no secret that WDW is giving serious consideration to enhanced FOTL access or superduper fastpass privileges to guests of deluxe resorts (or perhaps as DVC perks or cruise perks).
The artificial inflation of hotel rates and elimination of discounts -- even if revenue reducing in the short term -- is a very natural first step for this kind of move.
Sorry for such a long winded and nerdy post; it will be interesting to see how it plays out.