Changes in SP's speaking voice

Has anyone else noticed that Steve's speaking voice changed in pitch & tonality over the years (never mind his singing voice)? Now mine has changed too but I blame it on my nasty little smoking habit. Mine got deeper, more gravelly. If I'm not mistaken, Steve's got higher.
If u compare his speaking voice here: http://www.youtube.com/watch?v=UD6Cil4_5_Y (1983)
w/his voice here: http://www.youtube.com/watch?v=BUPoSXgzHow (1986)
then here: http://www.youtube.com/watch?v=b5swl3jZGaU (1991)
then here: http://www.youtube.com/watch?v=62DpVKF1-4g (2001)
& then listen to his interview w/UJ last week, doesn't it sound like he gets higher & higher? Not just more raspy, but actually higher pitched?
So, my question is, what would cause that? Aging, voice abuse, some kind of surgery for polyps? Any thoughts?
If u compare his speaking voice here: http://www.youtube.com/watch?v=UD6Cil4_5_Y (1983)
w/his voice here: http://www.youtube.com/watch?v=BUPoSXgzHow (1986)
then here: http://www.youtube.com/watch?v=b5swl3jZGaU (1991)
then here: http://www.youtube.com/watch?v=62DpVKF1-4g (2001)
& then listen to his interview w/UJ last week, doesn't it sound like he gets higher & higher? Not just more raspy, but actually higher pitched?
So, my question is, what would cause that? Aging, voice abuse, some kind of surgery for polyps? Any thoughts?