Of course the studio tracks are doctored to a certain extent.

However, stuff like Autotune, Melodyne, reverb on the vocal etc. doesn't magically induce rasp to the vocals. He has infinite takes, can take time off, drink some hot tea, warm up, and do ONE SINGLE raspy line in the studio. Live, if he messes up a raspy line, he potentially damages his vocal chords for 3 seconds of live entertainment.

In the studio, those moments are documented forever. Going to his limits vocally pays off much more, so to say - it's there for more than just 3 seconds, but part of his legacy. And he doesn't have to go straight into the next line after a scream or raspy line, but instead, can take the rest of the day off (I'm exaggerating, but you know what I mean).