The Disney Dining Plan is not available as an a la carte add-on. Unless you are a DVC owner who is staying at a DVC resort using your points, then the only way to purchase the Disney Dining Plan is to book a package.
Yes, it's true that Annual Passholders do not have to purchase tickets as part of their dining package, but yet it is still considered a package by Disney. This may be important to some people, as the cancelation terms and payment terms differ between room-only reservations and packages. A room-only reservation requires a 1-night deposit and then the balance is due at check-in. A package requires a $200 deposit with the balance due by 45 days before the trip (if you book the package fewer than 45 days before the trip, then the full cost of the package is due immediately, at the time the reservation is made).
In other words, Annual Passholders who like to or need to wait to pay for the trip until the time of check-in are out of luck if they wish to book the Disney Dining Plan.
And as you've already learned, non-DVC members and non-Annual Passholders who wish to purchase the DDP must do so as part of a package. This sort of package MUST include at least a minimal ticket purchase of a 1-day base ticket (but of course it can be a bigger ticket, as well).
A 1-day base ticket costs $82. You will have to pay this in addition to the daily cost of the DDP. In other words, you have to pay an $82 premium per person just for the priviledge of being allowed to buy the DDP. This eats into any savings you hope to realize by buying the DDP versus paying out-of-pocket.
Edited: 19 October 2010, 23:16