There could be a number of reasons. He could use a wireless router for a more convenient connection to his computer. He could connect other devices besides a computer to his router, such as gaming devices. Many routers provide built-in protection against intruders and so forth. He may want to have more exact control over his network operates and how his bandwidth (a measure of the capacity of his connection to his ISP). He may use or soon want to use a Skype connection as his phone (it is a VOIP type setup, you can google if you want to know more). And there are probably a few others I am leaving out right now. Any computer geek would have a router, even if they only have one computer.

rafi