Vibrato is not something you control, it just happens because of the air and technique...it's actually quite hard to "fake" it, so I honestly think that he changed his singing technique for a healthier one, more similar to classical singing (which is supposed to be the healthiest one of all for your vocal chords).
His belting is weird, like I said before, and I think that he has been having problems with his vocal chords for some time now, and when you feel uncomfortable, you start doing weird things to "mask" it, or to not feel pain, and that makes you change the way you sing, usually taking up some bad habits...and those are hard to change back, it can be done but he would need to work with a professional to do it. That happened to me last year...I had a problem in my vocal chords and I had to learn how to speak properly again, it took me 4 months to get my voice as it was before.
Of course drug abuse, alcohol, cigarettes will damage your voice, but I don't think that's the case here. Maybe he could have lost some high notes because of that, but I think this has more to do with exhaustion and bad phoning more than anything else.
Sorry about the long post, I sound like a school teacher here, but singing and the voice is something I'm passionate about, as you can see...xD
