Do you really believe that creators and copyright owners have so much time on their hands that they will spend it sending out unnecessary notices? In my opinion, if they take the trouble to report a possible infringement, it's because they have serious suspicions. Furthermore, in order to use a work, you have to request the prior authorization of the rights holder. If the rights holder has not given his or her authorization, there almost certainly is infringement of copyright. People do not just get up one morning and decide to send out dozens of notices for no reason.
On February 10th, 2011. See this statement in context.