I ran across a useful article at InfoWorld on the business case for using open-source software. The author describes what sounds to me like a nightmare:

... a small auto insurance company that we recently did some work for [uses] a custom CRM application that is designed for small independent auto insurance companies. It's a special application that nobody has the source code for other than the vendor, whose technical division is located in Alabama. Our client has to get a license key from the vendor each month and enter that into the program, or else it will stop functioning.

Get a license key from the vendor every month or your data disappears? No thanks. Keeping control of your data is a huge advantage of using open source.

Another advantage is being able to find people to maintain your software. Developers tend to like open source platforms, because if they don't like something, they can fix it. If your website is built using widely adopted open-source developer-friendly software, you won't have any problem hiring someone else if your original developer disappears. That makes it safe to hire small companies (like us!).