I'd argue that the CEO really should be a subject matter expert for the business domain. They can be ignorant on how it's all put together, that's the CTOs job, but they really should understand the domain.

I think the thing that confuses people is that the true domain for some companies isn't what the end consumer sees. I worked for a car website for a while, and very few of the executives were really car people. But they were all incredible experts on how dealerships worked, and that was actually what our business was, not how cars work.