Even on the These Days tour he couldn't hit all the notes he could 10 years before, specifically on songs like Livin' On A Prayer.

I suppose that because he virtually wore out his voice on the Slippery When Wet and New Jersey tours that could have had a long term effect, and also the smoking doesn't help, and probably just the main thing is age. He's been doing it for 20 years now, and even though he can't hit all the notes or sing quite as well now, even now he could probably beat most of the acts in the charts, who can't sing to start with and rely on their looks for record deals.