i believe that is semantics.
disney's real problem is they don't have fresh or enticing offerings at the other three theme parks to hold a guest's attention. i don't want to speak in broad generalities, but it stands to reason that if you're doing a theme park-oriented central florida vacation, the magic kingdom will be included. what guests do on the other days, which recently, has been visiting universal studios instead of epcot, DHS, and AK, is what i believe they are hoping to avoid with this ticket.
the average vacation to disney has to be in the 4 days-to-a-week range (
@ParentsOf4, any data on that?). maybe you could argue the average DVC member is a little longer. but what you're essentially posing to the consumer is this: give us a guaranteed day (doesn't have to be a full day, but you're incentive for it to be with no park hopping ability) at each park, we'll give you a discount. i believe that internal hope is that if a DVC family, who is probably used to doing some days that do not involve the parks (pool day, miniature golf, DTD, etc.), will look at each other and go, "wanna go to universal?" they'll ultimately come to the conclusion : "nah, i've had enough theme parks for one trip." disney then gets the added bonus of spreading out the crowds and goosing attendance figures at the other parks.
again, that's my read on it. i don't think disney care as much about keeping you there a full day (though they'll take that, too) as much as they care about you hopping on I-4 for any period of time.