I think you're splitting hairs a bit. I think a lot of DVC owners were making at least annual trips to Disney World before buying in to DVC. It is very likely they would have kept making annual trips to WDW anyways with or without DVC. For those people, DVC is saving money.
There are also people who buy DVC and it changes how often they go to the park. In a way, it still saves these people money since they would be paying to stay on site anyways.
There are also some people who buy in to DVC who probably shouldn't.
Bottom line, there are people where DVC definitely saves money. It just depends on the person.
But that ISN'T splitting hairs - its the whole question of risk. If you are going to ignore risk, then the math is going to lie. In fact, that is probably the biggest way to get financial numbers to lie, ignore the risk. The second biggest is to underestimate or overestimate the time value of money - something the DisBoards gets a gold medal in.
That doesn't mean that DVC can't be a good value. And some people save money (I think its pretty rare because I agree - there are reasons that Disney loves DVC and one of them - but only one of them - is that it makes them more money than not having it - otherwise - build more $500 a night hotel rooms). But in my opinion, its always best to be cautious when giving financial advice to strangers - that includes downplaying the opportunity for savings. If you really want DVC, it works for you, and can afford it, then if you save money or not really isn't a question that needs to be asked - its a fun question to ask, and I can - legitimately - either save money or spend much much more - depending on what assumptions I make and what techniques I use to get an answer.