He might not know how to make a game? He might not be a programmer or an artist. He is talking about game design and just designing a game is a job in the industry. If he doesn't know these other skills then he needs to get his idea across to people who do, which is why a detailed game doc is handy.
I disagree. My point is he should get the skills of a programmer (or an artist) first, not to learn how to get his idea across to others. As for designers in the industry, they *usually* don't code because they don't need to, not because they don't know how. Besides, when I watch these videos of "making of the game" I notorously see a designer coding a rough prototype to test a concept all alone. Personally, a computer game designer who don't know how to code is a nonsense to me...
I realize many people disagree with my opinion
Brenda Romero gave a talk at GDC a couple years ago (well, she gives one every year but this particular one was a couple years ago at the education summit) where she discussed hiring practices. In a nutshell, resumes of designers that can program go into the keep pile and designers that can't go into the trash. The game industry is a highly competitive field and if presented with two candidates for the same job the one with better qualifications is more likely to be interviewed. If you can't at least do some scripting, you're going to have a hard time with the design test most companies will give you as part of the interview process.
To pull an excerpt from the Valve Handbook for New Employees:
"Non-Engineers: program or be programmed
Valve’s core competency is making software. Obviously, different disciplines are part of making our products, but we’re still an engineering-centric company. That’s because the core of the software-building process is engineering. As in, writing code. If your expertise is not in writing code, then every bit of energy you put into understanding the code-writing part of making software is to your (and Valve’s) benefit. You don’t need to become an engineer, and there’s nothing that says an engineer is more valuable than you. But broadening your awareness in a highly technical direction is never a bad thing. It’ll either increase the quality or quantity of bits you can put “into boxes,” which means affecting customers more, which means you’re valuable."
Edit: I added a link to Brenda's rant on her blog. Check it out.