Everywhere I've ever been, "black & blue" in relation to steak has always referred to a healthy dose of black pepper, sauteed mushrooms and blue cheese melted on top (which is my absolute favorite way to have a steak, by the way).
The "pittsburgh" term originates from Pittsburgh steel workers. On paydays, many of them would buy themselves a thick porterhouse steak as a nice self-reward, take it to work, and slap the steak directly on the super-hot iron, and then eat it for lunch. Charred on the outside, bloody rare on the inside.
Of course, it can only be done right with a very thick steak.