Personally I like this style of cut. Maybe the problem is the word mullet, since it seems to have taken on a negative sense. Perhaps camaro, hockey hair or a Canadian passport have a better connotation.
A lot of my favourite recording stars have had a camaro cut at one time or another--Neil Diamond, Paul McCartney, Suzi Quatro, David Cassidy. The Guess Who wore their Canadian passports proudly in the late '60s. Derek Sanderson had great hockey hair when he played for the Bruins in the '70s--I used to marvel at it, watching "Hockey Night in Canada" with my dad and brother.
The period in which Superman had the long hair maybe wasn't the best time for him as a character. Things got worse for him when he went electric. So I'm guessing some fans associate the Kentucky waterfall with a drop in quality.
And what about Nightwing? It seems like he never has had to pay for his nickelback the way Superman has.