Create a two exact rectangles and choose one and punch in .5 in the corner radius from the tool bar. Now on the other use the Fillet docker and punch in .5. Center them over each other. When viewed in wirerframe and you will see a noticeable difference on the corners. Not enough to make a big deal but I would expect no difference.
Myron, It might amuse you to throw a circle (ellipse) in there at the appropriate location. Then, you will see yet a third radius that isn't quite the same as either of the others. The differences are too small to make me lose any sleep, but I find the observation interesting.