DC and Marvel properties have been selling for years. Throughout the years, various characters have been introduced. Superman first appeared in 1938, donning a costume that would have not been considered well designed by modern standards of fashion. His costume evolved, but remained similar to the one he donned in his debut. Some characters saw greater costume changes, permanently or temporarily. Spider-man wore black. Daredevil added grey to his usual red. Wonder Woman, Aquaman and Thor each saw a wide variety of costume changes.
And when comics put a hero like Spider-man or Captain America in their classic costumes, alongside a member of the Young Avengers, you not only see superheroes of different eras coming together, you also see the design sensibilities of different eras placed side by side. The fashions in the Marvel and DC universes are a mix of past and present designs. Superman's costume is far from tasteful if someone came up with such a design today. Look at Invincible (Image Comics), and the way the superheroes and villains are costumed. Many bright colours, but with hardly anyone wearing his or her underwear on the outside.
Updating costumes are a must for some characters that were invented many years ago. Changing iconic costumes may not go well with many fans, but they are a must if characters are to keep up with modern times. Superman lost his outer "underwear" once, when he turned blue (as well as red at one time). And looking at Jim Lee's designs for the upcoming company wide reboot, Superman will lose that iconic piece again. I hope they restore it.