Could be you don't have rebar being used in MA residential work. I tied off rebar for a whole summer, but that was in New York City and commercial work at that, and am not familar with residential practices up there. I've got a block foundation and put rebar in the footing myself. I still would not recommend weakening a corner, rebar or no, but could be wrong. Concrete has a lot of compressive strength to support weight, but not a lot of tensile strength, resistance to shear or bending. Solid corners would appear to help prevent the latter, and foundation cracks. Someone correct me if I'm off base here. I do tend to overbuild and exceed code requirements.
Mike
Mike