It's not a matter of being open source or not. I think his argument is that you can make money without copyright. Regardless if you open source your software or not. And not only you "can", but it's also the most profitable choice of today. You pointed to the gaming industry, which is an interesting example because our industry is moving toward free to play exactly because copyright haven't been paying off recently. Although I'd argue companies are doing this extremely slow because of their own bureaucracy and incompetence.

So my answer to your question of "do you think they would be making as much money without copyright" is that they would be making much more without copyright.