Yepp. It's 100% his voice, his grit. Did you hear the Cry snippet where R. Kelly can be heard too?
http://soundcloud.com/pentum/shoulder
yup i heard it i didn't even know there was ever a question that was mj. u are right, it's also definitely r kelly.
edit: i don't think it's any big deal that r kelly sings some words in OMC. it's just supporting vocals, same thing as with butterflies. mj probably just included it because he liked how it sounded. i honestly don't even see a difference between that and something like "it's the falling in love"--mj didn't sing every line of that either, what's the difference?
the cascio tracks are completely the opposite of this though, in every way because
1) michael is gone, the artist is not here to make conscious editing decisions like that.
2) it's not like michael is singing 95% of the song. he's not on ANY of the lead vocals, and is, in fact, only in the ad libs. it's flipped
3) kelz was probably IN the studio, I doubt it was a copy/paste job.
4) r kelly is one of the best singers in the entire world. (my opinion). He's a very well respected artist in his own right. JM is not.
OT: if you haven't seen the Light It Up Tour DVD by r kelly just get it. It's sooooooo worth it. The man has hits for DAYS. ridiculously entertaining.