For better or worse, I think Basecamp started this trend. Not necessarily with the content they have created and sold, but with the ideas that get misunderstood. I think it was Jason Fried who said people should be selling their byproducts, which amounts to remixing content, selling what you’ve learned to others. This works and is good practice for some things, but it gets extended into so many other things that we get an “information product” economy where the information is the only product instead of the information being a byproduct of the experience you gained by building something else.