Sunvox-- you may have old information. It used to be that Delta pilots would have to send a message to say they are not extending, it was otherwise assumed they would. The FAA started asking why we had more extensions than our peers and as a result this practice stopped. Now when your duty is close to requiring an extension, we are asked whether or not we are willing to extend and there is no paperwork or jeopardy if we choose not to. At least in my short time here, the vast majority of Captains I've flown with have a default position of never/seldom extending.