So using Concierge, I would think that Disney Restaurants save bookings for Concierge. It would be interesting to see, if you would gamble with your family trip... walk in at Disney restaurants and see if you could get a table. I doubt it. The majority of the world does not use Concierge! I have read posts, where Concierge CM's will call the renter and see what all they can pre- book for them, is that true?
Even though we have DVC, whenever we wish to visit WDW we book conceirge so we can take advantage of all the extra help we receive for our ADR's and firework shows. For us it is still so worth it, just due to scheduling, timing and airfares.