Nono, you've got it backwards. The Nagato thing is easy to explain, Sasori is the perplexing one.
It brings you back in the state you were a little before death, or at the exact moment that you died, either way.. Nagato still had his eyes (And was still crippled) before and exactly when he died. It wasn't until a while after his death that his eyes were taken out, so that's why he's that way after Edo Tensei. He's the way he was before/when he died.
Sasori is harder to explain, and I'm not sure if there is really an exact reason yet.. but I have a bit of a theory. Sure Sasori's heart was still beating when he made his own body into a pupper, but was his soul in there? Or was it.. y'know, passed on, as if he were dead? I mean maybe when he turned his own body into a puppet, and had only his beating heart remaining, that was the moment that he "died"? Because then he would look normal, and not be just a heart. Right?
..Ah hell, I don't know. Until Kishi gives us a solid explanation, I guess I'll just stick to my "He figured nobody would care/notice the Sasori thing" theory.