Interesting theory. I do think aging and smoking have something to do with the fact that Jon's hurting his voice a bit. Smoking is bad for your vocals, this is just a fact.

Jon's studio voice is always better than his live voice, this is just the nature of the beast, you use the best take.

I am convinced that Jon alters his singing style simply because he can't be straining his voice just like he used to in SWW or NJ days. The new style is not better or worse, it's just different and is probably good to save his vocal cords.