Then, how do you decide where to cut off? Your statement can be said of virtually every site on the web, whether shopping or not. Every retail site only contains content (items) from some manufacturer. How can any retail site be included, their content is not original. What makes one worthwhile (or valuable) and another not?
I could also argue that the content of the ODP is not original, as I think you would agree. What can make it worthwhile is how you put it together. That is the aim of our site, to package the products and their associated information in a different way that we do not see duplicated elsewhere. It carries our experiences as teachers and researchers into the methodology.
Information exists in abundance on the web. Finding it, and all that you want to know, is another matter. That is our long range goal - to explain (to the level each individual wants) each item that we sell.
As a personal side note, I concur that the ideas in my explanations and tutorials can be found elsewhere. However, I prefer the way I do it or I would not bother to write - anymore than I would have done the three years of work to write the modern physics text my classes use.