I don't see those comments as out of bounds at all. The man is 47 years old. That comes along with certain things for most men, including thinning hair. This isn't the 1980s where your sales were directly proportional to your follical prowess; I think if JP cut his hair short (and it looks good on him when he does), a lot of people would probably say "finally!!".
I dunno; to me, when a long-existing band starts cutting their hair (e.g. Rush), I see it as a sign of maturation. It's essentially saying " yup, we're not a band in our twenties. We do this stuff for the love of music, not to keep up some pretense. ". I find the longer DT tries to run this " ZZ Top in a biker bar" image, the less believable it becomes. MM's caked-on hairdo during the ADTOE tour was reaaaally stretching it. Especially when he had such a likable hairdo during the documentary.