You'd think DiDio would've lost his job by now, considering all of the restructuring that's been going on at DC lately.
DC's problems really go beyond DiDio if you ask me.
Wonder Woman's problems have resulted in Heinberg being unable to turn in his scripts on time and Amazons Attack certainly didn't help much.
Characters like Aquaman and Hawkman are regarded as a jokes due to past interpretations of the characters, hence why DC is reluctant to make books on them. Getting big name writers like Geoff Johns (who is rumored to eventually take on Aquaman), Grant Morrison, etc. can help fix that.
Superman's biggest problem is the simple fact that Superman doesn't star in his comics for the time being. I think that was a risky gamble on DC's part and it failed. I think things will improve on that front in Superman #700 where Superman returns in the book freaking called Superman.
DC's characters aren't being promoted properly due to the ineptitude of Warner Bros. (who are poorly promoting almost all of their characters like the Looney Tunes, Hanna-Barbera, etc.) which doesn't create as much brand recognition that there should be. DC Comics' restructuring into DC Entertainment is supposedly meant to deal with this aspect.
And this is a problem for Marvel as well, but I think that DC really needs to improve upon distribution and obtain more licensed properties. Disney and Warner Bros. should try and obtain smaller publishers like Boom (which holds the licenses for Pixar, Muppets, and Mickey Mouse characters, making it a perfect fit for Disney), Dark Horse, Dynamite, etc.