It's not like he's selling Prince of Persia or Command and Conquer t-shirts, or a book on how to rip off games and make money doing so, he's selling expertise o

It's not like he's selling Prince of Persia or Command and Conquer t-shirts, or a book on how to rip off games and make money doing so, he's selling expertise on creating game engines, and using retro games to demonstrate the effectiveness of the techniques. He's doing this out of a love for the games in question, evidenced by the faithfulness of reproduction. What you're describing is something like Evony or Zynga, where they rip off other games wholesale and pretend it's original. There is a reason why practically every indie engine under the sun has the ability to load e.g. Quake models. It's an easy source of well-crafted content. Programmer art is a surefire way to kill interest in a project.