Listen, I'm not saying your systems don't work. I'm just saying they are still far from perfect. And still so close to their predecessors.
People writing textbooks these day understand the people will read them on computers and iPads. But they don't change anything. We read ebooks, but they are EXACTLY the same. Sure, they work. But why don't they work better.
Like I said, why don't they incorporate videos? Customized problem sets based on what I don't understand?