I know that Blender did it, I can see from the wireframe that you've used quads. I'm just saying that you probably wouldn't be hearing people complain about the hard edges if you could get it to render as quads. I've never used Blender so I can't tell you how the smoothing groups or whatever it uses work, but for me, it's hard to get past. The wireframe actually looks the best of the four images.