Gratuitous character remodeling
Johnny Depp as Tonto is a very egregious example of what you describe, John, but a few others spring to mind. No Chinese actors were available to play The Mandarin in "Iron Man 3," eh? I love Ben Kingsley as much as anyone, and in fairness the character he ended up portraying was a far, far cry from the source material, but as soon as the casting was announced, I couldn't help thinking it was a lost opportunity for Asian actors who would have loved such a meaty role in a summer blockbuster.
And I couldn't help but notice Khan Noonien Singh was suddenly looking rather pasty and British in "Star Trek: Into Darkness." Once again, love the actor, but what the hell, Hollywood? (I still think that movie would have worked a lot better if an original character with the necessary background had been created for Benedict Cumberbatch to play.)
I'm not a stickler for this type of casting, but the people who run Hollywood are big supporters of race and gender-based quotes for everyone else's industries. (And it gets even harder to swallow the hypocrisy when you look behind the cameras.) Also, some characters are defined by their physical attributes, such as Tonto being an American Indian; others have physical attributes whose gratuitous re-wiring can seem annoying to fans. Maybe Johnny Depp will really knock this out of the park, but Tonto seems like an awfully iconic role to play this kind of game with. Although I can't say I've heard much in the way of complaining from the grievance groups that keep deciding decades-old sports mascots chosen to honor the skill and courage of the team are suddenly racist insults.