Yes, when you strip away the complex characteristics that make a comic book hero who he or she is, you get just that. But what defines a universal example of humanity? The differences, the ability that humans have to exist within their own spaces and within other spaces while remaining individual is what makes any character readable. If you have a group of characters all searching for the same thing, then the things that differentiate them are those qualities: social, cultural, political, spiritual, etc. Essentially those qualities that are considered become strong contributing factors on how that person becomes a universal concept of humanity.
No, those qualities are part of what define them as individuals. Even you say that they are "things that differentiate them"; therefore, they are not universal qualities.
There's been a huge shift in literary thinking from the mid-20th century to now that has taken place on the individual reconciliation of the fragmented identity. When I say "fragmented", I mean the elements that make a character's struggle significant are in pieces and often the protagonist contends within his or herself to reconcile social, cultural, political, spiritual elements in his or her life. It works well in literature. It would probably work well for comics as well if comics were being held entirely in literary regards.
Unfortunately comics, mainstream comics especially, are still a business. They have to connect with a large group of people and sell high numbers of they are not successful. When they fail to connect with the large, target audience, then the company writes it off. It's just not a successful idea to market.
If this is "not a successful idea to market", then why should they bother creating anything other than middle-class straight white 30+-year-old guys?? That is their target audience. Heck, why did they bother de-aging the characters for the DCnU?? After all, many of the characters were already the correct mid-30s age for their audience.
Why create their BFF Nu Beetle, the far-less-than-30-year-old Hispanic, and back him to the point of giving him a series TWICE??
Why go through all the trouble to borrow Static from Milestone??
(Dwayne McDuffie said they wasted HIS time; who knew at the time that they wasted theirs, as well??)
And man, they really should have dumped that part-Chinese, part-Arabic Robin, Damien, long before last month! After all, according to you, there's NO way he caught on with many of the Bat-fans!
Believe it or not, such diversity characters CAN connect with the white target audience. John Stewart's stint in the animated Justice League and JLU managed to make HIM the "One, True Green Lantern" to many non-comic readers. The aforementioned Static managed to get FOUR seasons of Static Shock, and would have gotten MORE if the toy companies didn't think like you, and panicked at the thought of marketing a toy of a black character to an audience that largely isn't black. And that idiocy happened even though the audience already proved that they love the character!
The bottom line is that you don't know that non-white, non-straight characters won't connect with a large audience until you TRY. One thing that I can actually compliment Dan and the Gang on is that they do give "diversity" characters a shot. The problem is, they've handled them in the Typical Slipshod DiDio-era Manner... and that's why the major key to using non-white characters is that they must be handled WELL.