Check the "Ball Blue Book" book on preserving. They have (in my edition from 2009) a (very short) section on "low sugar, low salt" recipes. Mainly they recommend using sugar substitute instead of sugar, or cutting back on real sugar, or none at all - for the reasons given above; sugar isn't necessary for the safety of canned fruits. The Ball/Bernardin site probably has the same information.
I also don't understand the addition of sugar to many recipes, either for canning or just for dinner. I was astonished to learn some while ago that many people seem to believe that sugar is a necessary ingredient in spaghetti sauce. But then, I've never particularly liked cooked tomatoes, so usually ate my pasta with a herb & butter sauce ... So what do I know? LOL. I've always been one to play around with the sugar/salt/herb/spice quantities in recipes (NOT when it comes to safety in canning however)