I agree, it has been happening a lot, but look at the results. Daredevil sucked, and many people weren't happy about the change to Kingpin. Hulk's gamma bomb origin has nothing to do with his appearance, which is what I'm referring to here. X-Men isn't exactly a blatant violator, since the majority of the characters are still easily recognizable at first glance. And Joker in no way reflects what i'm saying, because he still looks exactly the same, all that's changed is the REASON why he looks that way.
Now, realistically, if you just gave a black guy a skin condition, without reptilian scales, would you be able to immediately recognize him as Killer Croc?