Delta did have DEQMs in the spring last year, but unlike the competition attached some stipulations to it (as in L/U/T fares didn't count - everyone else allowed all paid fares to count).

Last year, US was the first to launch it, but it wasn't till AA launched theirs a month later that UA (and then DL and CO) matched. In the fall, it was AA that started it, followed by a UA match, then CO.