Thanks everyone for all your insightful responses. As for my opinion, even though I don't know much about it, I kind of understand why they westernized it, but also think that they're kind of not caring what the real fans (you know, the people that made it popular) think about it. But on the other hand, apparently there is a different Death Note movie out, it has an entirely Japanese cast but I heard that it's good. So, maybe they figured the original fans already had a movie based off the real thing and so the American version is more for the people that don't know about the anime and manga. Just like what @zoop said, they're making it for the basic people who don't care what happened in the original and just want to see the westernized version, and I can understand that.
Anyway, thanks again for your guys' replies! I really appreciated them.