I'll personally admit that I far preferred the new Heimdall but I didn't really have any preference or knowledge of Heimdall from before. Samuel L. Jackson (or Lawrence Fishburne if I were to repeat that idiot radio show that confused the two with Samuel L. Jackson on the line...) is an amazing choice for Nick Fury. I mean, I'd heard of him and seen him in practically every cross over but I didn't really care about him or follow his story.
But let's be honest. These are generally not the big title characters. Shredder is. He's the main villain. How many people do you think had actually heard of Heimdall before that movie? How many non-comic book readers had heard of Nick Fury? These aren't the characters that have spread into larger pools of knowledge. These are niche characters that were ripe for changing come mainstream.
I'll grant that Shredder was also a little more specifically Japanese. What with the martial arts and teams of Ninjas it would be a little extra weird to make him a white guy.
Also. if white male wasn't the dominate actor in films and television, you'd have something of a point.
Wait, you mean in the US media where the US population is over 72% white (includes white Hispanic) that the majority of the actors are white too? I'm shocked and appalled, the nerve of them! [/sarcasm]
A fair world has proportionate representation. It does not give more representation to any group than its size warrants. You don't see me watching a Bollywood movie and complaining that there aren't enough white people. I get it, people are Indian there. They aren't being racist in casting the most common demographics they have there.