That's nonsense with respect to books. If you self-publish on the most popular distribution channel (Amazon), you keep quite a large percentage of your revenue. The issue isn't the middleman, it's that there's a huge number of other books out there and unless you already have an audience or put the work into creating one somehow, not many people are going to find your work and buy it. If lots of people actually do buy it, you get a pretty good cut. But it's hard to get to that point.