I use "douchebag" for those for whom status and money are top-tier goals, and those who are willing to make ethical sacrifices in order to further their career and material well-being. People who fit this profile tend, in addition to being shallow, to be relatively useless because their only skills are political play.
My investment banking peers were some of the most outstanding people I've ever met.
I've met some great people at all levels of investment banks, but there's no denying that (except outside of a few ivory-tower quant groups) investment banking has a douchebag culture. Face time, moronic machismo, authoritarianism, and professional hazing all play into that. Most of the well-adjusted bankers have an almost heroic ability to keep themselves centered in spite of their insane environment.
"Douchebags" seldom get anywhere in business unless they're related to someone important [...]
This is generally true in technology, but not as true in business as a whole. What underlines a douchebag-friendly environment is one crucial element: opacity of contribution. Douchebags generally spend too much time playing politics to contribute under their own power, and usually get ahead by taking credit for others' work, assigning themselves (and people whom they know will let them take credit) easy but important-seeming projects, and playing politics. In technology, it's harder to pull this off than in most other businesses.
You're also confusing "asshole" and "douchebag"-- two related but distinct concepts. An asshole is a mean, obnoxious, and tactless person. A douchebag is a socially successful and smooth, but mean-spirited and worthless person. Assholes are assholes to everyone and generally reviled for this, but douchebags aren't douchebags to anyone important, and will only be mean if it improves their social standing. So you don't necessarily know, in all circumstances, who the douchebags are. Douchebags climb corporate ladders easily, due to the opacity of douchebaggery. Assholes, on the other hand, almost never rise; if no one else takes them out, a douchebag will, because the reviled asshole is an easy target.