If you are referring to the Disney Dining Experience card where passholders get 20% off food and drink at most sit down restaurants, then it is valid for all meals.
I think you may be confusing three things (which is very understandable since the whole thing seems a bit too complex) :
The MYW Dining Plan - Only available to people who book full ticket/room packages, costs about $35/pp per day, gives you 1 counter service, 1 sit down, and 1 "snack" per day.
DDE - Disney Dining Experience is a membership/card that used to only be available to FL residents and is now open to ALL passholders as well. It gives you 20% off your entire meal (including drinks) at most sit-down restaurants at WDW and a few counter service (the food courts at the All-Stars and Pop, as well as the counter service at AK ). It costs $50/year and is valid for breakfast, lunch, dinner, and character meals as well.
Regular AP Discounts : At select dining locations (most of the sit downs in World Showcase and at Resorts) Passholders already get a discount at lunch only on weekdays.