Mutt, quite correct, nothing to do with all eng's operating, however in many cases all engines are assumed, SID's are not as you say constructed for the a/c with one or two eng's out. They are obsticle or noise routes the former tends to list a min climb gradient to a certain height as you know. Now for the scary bit, who knows what there a/c will achieve/climb gradient, and I am not of course talking about the minimum gradient requirements, I am thinking about an eng failure half way through a sid, eg leaving 1700 for 8000.
Best Rgds