Not all websites follow a definite pattern. They can be a combination of website types with a central unifying theme. This type of website is often spawned from a existing site which branches out from its original mission to include some supporting material to further enhance the visitors experience.
Business sites are the most likely to support this concept of multi tasking. Often a commercial website will offer more than just product information. They might include a section devoted to the latest news or provide discussion groups/forums that are geared to a particular subject related to their industry. Another combination might be a news site that sports a section for the entertainment of their visitors such as games and/or jokes.
Also, many websites have a feedback area to allow visitors to voice their opinions and comments. This is often in the form of a forum or a discussion group centered around the main topic of the website.