I have read Brian's post, and he does leave this particular info out. How do you know there is not the demand when there is not the supply?
There is supply, it is increasing relative to demand, and you can measure it. As DVC grows, more units get deposited. That's not because individual members are depositing more often, but because there are just simply more members. Unless demand keeps pace with that growth, the supply/demand curve slips.
I've searched DVC nearly daily for almost two years. Even in that short time, the number of units in the "leftover" pile each morning (after ongoing searches have matched) has grown noticeably. It's more common to see units (even 1BRs) in BWV and VWL in addition to OKW/SSR, where before you might go days without seeing either resort at all. I'll let others who also search II chime in with their own impressions, but that's my sense.
If you happen to be a member of TS4M, you can check this yourself by going back a few years' worth of posted Interval sightings, to verify or dispute my sense of things. One of the TS4M members posts Disney sightings nearly every day.
Now, to be fair, this increase in available units could just be because leisure travel is depressed right now. But, this trend reaches back to before the mid-summer gas price spike (and well before the fall stock market collapse). It could also be due to the heavy use of developers points that sound good in a sales meeting, but can't really be used before they expire, so they are deposited in hopes of a future exchange. Whatever the reason, though, the result is plain: there are more units not being taken by ongoing search, and that's not good for the supply/demand curve.
The DVC units, strictly on their own merits, tend to be "good", but not outstanding. I'd compare OKW to the better Wyndhams we've been in---nice appliances, but average soft goods, cheap countertops, etc. The quality of the hard and soft goods in SSR is better, but the unit size is small compared to similar non-Disney resorts. As an example, it's really sad that a unit that sleeps six privately, and eight maximum, has a table that only seats four.
Outside of the units, the resorts stack up nicely. Excellent pool areas, a nice slate of broader activities, excellent landscaping, etc. Nothing exceptional, but very nice.
But, what DVC really offers is the on-property experience. That appeals to some, but not others. It may not appeal to the "typical" timeshare owner as much as it might to the average family---timeshare owners are more likely to have older kids, or be empty nesters, and visiting Mickey is something that many people think of as something they do when the kids (or grandkids) are little. Worse, the Resort Services Fee means that an exchange into DVC is $95 more than an exchange into any Orlando resort. So, if you aren't there specifically for Disney, why pay extra when you can stay in a better-equipped, larger Marriott resort for less?
The advantage to RCI for DVC Members is that there is a larger base of people who might want to exchange in. That exposes the units to a larger demand pool, and DVC is absolutely unique---for those that want to visit Disney (as opposed to "Orlando" or "Florida") the DVC resorts offer something that none of the others can touch. While that's a niche market, the size of RCI's niche is larger than the size of II's niche, and that bodes well for the supply/demand curve.
Whether that matters---whether there are resorts that Members want to exchange into---is certainly up for debate. My personal experience with exchanging in the two systems is that in areas where II has sufficient coverage, the II resorts are higher quality. But, there are areas where II doesn't have much in the way of inventory, and RCI does. I'm not sure I'll retain my II account after DVC leaves the fold.
The one caveat to all of this: if DVC negotiates a 1-in-4 rule with RCI (and I've read a report that at least one RCI VC has said this this), it will artificially reduce demand for inbound exchanges, and while that's great news for Disney (increases sales traffic and provides another reason to buy) it's bad news for DVC owners who may want to exchange some day.