In my experience, most writers write because, well... they have to. There's sort of an inner drive that starts fizzling and popping inside your brain if you don't give it an outlet now and then.
Many writers, when faced with the reality that the creative process WILL happen whether they want it to or not, decide to make the most of the situation and turn their, ahem, addiction into a money-making tool. From Scalzi's post, it sounds like he falls into that camp.
No conflict between art and business, there. It's more like a harmonious and symbiotic relationship.
