The field of business is very large:
Sales, marketing, accounting, project management, finance, legal, strategy, intellectual property, human resources, presentations, customer development, branding, writing, business planning and more are all topics that good business guys understand well.
Add into that the market specific knowledge (manufacturing, regulations, distribution channels etc) and you have a pretty broad reading list.
Most do have pretty detailed domain specific knowledge from working in that industry in some capacity.
Tangent: Agreed, though hopefully < 30k.