I think you have two issues here. The first is that in a larger business there are a significant number of messages that get sent out as a matter of corporate policy that don't get the attention management thinks they should. Quite possibly email is not the best approach to these, but telling management that the email was a waste of time is going to make no friends, especially if there are legal reasons for the announcements.

The second problem is that there are managers who do send out de facto spam and probably could use the feedback.