After watching this (and finally watching the rest of the Tarrytown fundraiser beyond IWDYH), what bothers me isn't the quality of Jon's voice, per se; it's the way he suddenly can't seem to follow the melody. I've been thinking, all along, that it was because his range had gotten lower, and he was struggling to just reach the high notes, much less tune them beyond a certain point. That's not unusual. A lot of artists run into that when they age. But even on the lower songs, like the ones you mentioned, he's not singing on pitch more than half the time. LIS was almost completely monotone, with occasional shifts up or down one note from where he started; and in IML and Who Says he was just off-pitch in general. Missing a few notes here and there might be a range, vocal cord, or breath control issue. But missing more than you hit sounds like an inability to match tones.

I remembered reading that Derek Shulman once said when he first heard him, Jon "only had a range of about 3 or 4 notes and most of them were off-key" but he more than made up for it by being a front man whose star quality was undeniable. At the time, I thought he was exaggerating, but now I'm beginning to wonder.