WordPress isn't just for bloggers and small business. As of now there are over 25 million people using WordPress worldwide. They use WordPress to run everything from celebrity and mainstream media blogs to academic and Fortune 500 Web sites.
Clients sometimes wonder if WordPress is suitable for their needs. When they hear that it's free they may worry that it's not robust enough, or that it will go out of business. Showing them who else is using it can help to assuage their concerns.
When they see that major corporations trust it, they begin to realize that you're not recommending it for the price tag, you're recommending it because it is the best tool for the job. (That doesn't mean that WordPress is the solution for everything, but it does work rather well for many types of sites).