Err, while I don't know him, I'm pretty sure he went on record saying that it wasn't so much that he couldn't scream anymore as he didn't want to. He doesn't listen to that kind of music so why try and make it if you don't enjoy it?
While IDT were my favorite band, I'm even glad he left because now, through QCS I have begun to apreciate a whole different kind of music.
Don't any of you guys know that Nick left IDT because he can't scream anymore? :O
His vocalchords are damaged so he can only sing clean singing, thats why he's not screaming so much on Sirens. shiit, thought everyone knew.