Since writing is what my partnership focuses on, I`ll go ahead and chime in here. Yes, there is certainly a need for great business writing, both on the internet and brick and mortar situations. However, as Vapourlock points out, it is hard to call writing a true "business". Me and my partner actually provide all of our services, therefore we end up functioning more like a practice or firm.
We would like to someday get to the point of being a business. What I mean by that is an entity that makes money, even when we aren`t working. For now, we are working on our own efficiency to decrease the time it takes to finish projects.
We have considered sub-contracting jobs out to other freelancers but we aren`t sure that there is a margin. Particularly since we would only want to deal with quality subs, who probably charge close to what we make off a deal.
There is definitely a way to do it. We just haven`t figured it out yet.