That's if you don't plan on selling your contract after X amount of years, when there is still value. We plan on owning for ~20-25 years and then selling. I factor in a interest rate of 2.9% annually, with a loss of 10% at time of sale, in comparison to purchase price, minus an additional 8% commission to the broker.
That's one of those assumption that you can make, but might get you in trouble - part of the risk equation. If you sell during a down market, you may end up with significantly less than anticipated. I put all salvage value under "chickens not to count until they hatch" - and consider it gravy. DVC isn't a diversified enough investment to even out the risk.
I suspect we will sell when there is still salvage value in the contract, but my crystal ball isn't that good, so I don't count on it in any financial planning.
Plenty of people have made a bunch of money buying DVC low and then not needing their contracts during peak market time and selling at a gain. Plenty of others were forced to sell at a loss when the economy crashed.