Samesies

I'm not quite sure what is included in copyright laws these days since I, 1. have nothing to copyright and 2. am not a lawyer but I do notice things that are almost identical and yet still coexist. Obviously you can't take a product, reproduce it and then label it as your own, same goes for plagiarism, but what about taking a concept and slightly altering it so that you are able to market it in the same market but under your brand? What I'm talking about is products like Coka-Cola Zero and Pepsi Max, or Nintendo Wii, Playstation Move and Xbox Kinect. I feel as though its almost unfair that after Coca-Cola came up with the idea to market a zero calorie alternative that Pepsi is able to steal this concept and make money off of it. Whether or not Coca-Cola came up with the idea first or not is irrelevant because they were the original brand to market it to consumers. Is that not intellectual property?