It's not about ill will, if somebody WAS singing your melodies you would still want to be recognized for those vocal innovations of yours in some capacity, would you not?

At the end of the day somebody contributed to the making of that record and walked out of the studio missing a cut, that doesn't look good on anyone involved.
just kinda ironic too with the whole "I was handed over this pre-written song but over here I got in an oh OHHHH oh so I think I have done enough to merit the title of lead songwriter" thing I learned all about earlier today http://atrl.net/?t=570679

He did eventually do with the song what she and were not able to.