Also clients in rich niches can afford the QUICKLY increasing price tag of quality SEO these days. As Luka said, a yacht company can afford those $1,000-$4,000 links like soda pop. An SEO by himself might have the skill to perform high end SEO, but not the huge budget and zeal for risk it takes to spend top dollar on the kind of links that work well these days. This is why people around here still do SEO for companies. And many who do ALSO have their own side projects, so it isn't one or the other.
-ThopHayt