Plus, different types of businesses run different risks. If you rely heavily on SEO for search rankings, or--worse yet--if your entire business depends on ranking high for certain keywords and keyphrases, you're running a greater risk in the SERPs than an editorially diverse "organic" information site is.
The same is true on the PPC side. It wasn't so long ago that AdWords affiliate advertisers were upset by Google's crackdown on direct-to-merchant ads, and more recently, the AdWords forum was jammed with posts from advertisers whose campaigns had been whacked by the new landing-page Quality Score requirements.
Every business has risks of one kind or another. For that matter, so do most 9-to-5 jobs. (I was laid off from two well-paying jobs in my employee days. Today, my income is paid in four currencies from multiple sources on three continents. We each confront and control risk in our own way.)