You need DWR because if your jacket gets soaked on the outside, your sweat will no longer evaporate through the jacket.
It's unfortunate, too, because the Shakedry jackets are what Gore has been promising for 50 years: waterproof yet breathable. I have one, and I am going to be very sad when it gets retired. Packs small, completely waterproof (I've used for 50 mile running races and stayed bone dry), yet breathable so you don't stew in your own juices (see "50 mile race" above).