I may be misunderstanding your question, but it seems as though your "server" could be written as a one-request server and then you'd just start another one to listen when a request came in. If starting a new process is too slow, use a pool. Some versions of Apache use this method. It's not a panacea, but it does provide a way you could use to avoid threaded code entirely.
OK, but surely there are cases where it would be useful (I would argue necessary) to have a single process with multiple threads - when dealing with GUIs for example.
