I dont know the exact answer to this but I would assume that the curvature on the blade makes it deal with the stress better that is casued when cutting the curve. (possible allow it to manouver better too) A normal cutting blade is straight and will snap easier when trying to turn/ bend on a straight kerf cut.
I have done the abrasive wheel training to get my ticket for sites and they were verybig on making a point of how worng and dangerous it is to cut curves with a standard grinder blade.