Limin,
To answer your question whether people really have a team of several different people work on a web site, or even outsource different areas of the development, the answer is "yes."
Can most very small businesses afford to do this? "No." But larger firms frequently draw together a team of people to create their web site, and include optimization and SEO copywriting in the package. That's if they're net savvy, and understand the importance of doing this.
Many ignore SEO, or only start doing it when their marketing people, or others tell them, "We really need to do this..."
Other mid-sized businesses will have a beautiful site developed by a web developer, but the site sits at the bottom of search engines forever. After a few years, they then go, "Gee, maybe we need to optimize" if they've heard of it, and want to get more online traffic. At this point, they will hire a firm that optimizes, or ask a copywriter who knows optimization to help them "fix their site."
So in one sense, many firms split up the work a bit. They get their web site up and running, then realize that they aren't getting any traffic, or that no one is buying from them, and THAT'S when they hire in the SEO experts or the copywriters...
Best wishes,
Sheri