Well, I wouldn't say that. Most WDW DVC members learn early (sometimes the hard way) that if they don't get their reservations in early, they're as likely as not to end up staying somewhere other than where they want, somewhere other than the their Homes. Having said that, if they haven't made reservations by the 8 or 9 month point, they're probably not specifically waiting to make the reservations just before the 7 month point. They're probably waiting until much closer to their intended trip date.
I don't know, but I wouldn't be surprised to learn, that a vast majority of DVC rooms are booked either just after the 11 month point, just after the 7 month point, or within 3 months prior. The rest of the time, again I'm guessing, is probably pretty quiet from a reservations stand-point.