Therein lies the problem, we are making assumptions when data is not available. We just don't know the total impact if discounts were provided even one such as your Artiste Point example. The problem is I don't think Disney really knows either because there is a mindset that discounts to DVC members are bad and should be offerred only when necessary.
For the most part I disagree. The list of restaurant and shopping discounts--while small--is not a static, unchanging list. Locations are rotated on and off of that list with regularity. Disney certainly does have the ability to track any upswings in foot traffic when a discount is introduced and they know how profitability is impacted by the lower margins on discounted purchases.
Tables in Wonderland used to be available only to FL residents. About 4 years ago they expanded it to Passholders. I agree that they COULD offer it to DVC members, but at the same time I suspect they view it as one of the incentives to get people to buy APs in the first place (AND make multiple trips in a year, AND add more DVC points, etc.)
As stated many people are motivated by discounts. But again offering a discount doesn't mean Disney stands to make any more money. Let's say a family has a dining budget of $500 per trip. If DVC members received a 15% discount at all (or most) restaurants, would that family be inclined to INCREASE their budget, or would they simply dine more luxuriously on the same $500? I suspect it's the latter more times than not, in which case Disney has to spend more on raw materials and labor just to earn the same $500.
I agree that Disney could get more experimental with discounts to gauge guest reactions--things like offering the TiW to DVC members or increasing the number of locations which offer dining or shopping discounts. But the main reason they will never do that is the backlash they will suffer in the event that such discounts are found to be unsuccessful. For instance, if DVC members were to gain access to buy the TiW and it was determined that AP sales suffered, that perk would be removed. Then Disney would face the loud chorus of "there's another DVC perk they took away from us!!!"