Just like in the case of Steam, I'm more apt to believe it's sellers that are doing this than Amazon. While both stand to benefit, sellers stand to benefit much more overall.
Although it's never going to be perfectly accurate, I recommend anyone who shops Amazon for expensive stuff use a price tracking service, like CamelCamelCamel, to see exactly how good a deal on Amazon really is. Again, not perfect, but at least you can then get some context for what the price is currently showing up as.