With a login operation beening done, and the server seems to accept this. The user from his pass experience, would expect an logout operation when he finish his work.

From an interface design or psyc. point of view, the logout operation is necessary.

Even it is 100% safe, without a logout operation, the user never feel safe. Even, it does not do anything, put in an logout link to save the user from a possible nightmare. Rgs, Kent Sin