There are a number of tricks people try to pull, and I hate them. Today's trick is one of the many varieties of the BCC trick (sometimes less surreptitiously—but still annoyingly—done as a CC trick).
Occasionally, I will be quietly added to an email discussion, typically via BCC, without any indication as to why I was added. After reading the discussion (which can be quite lengthy), I realize that they are pulling the "Raymond didn't deny this, so I'll assume this is true" trick. They are adding me as a way of obtaining my approval for a claim made in the discussion.
"The Widget does not immediately fire a ColorChange event if it has been hibernated. It will fire the ColorChange event when it is resumed." (Secretly BCC'ing Raymond for technical review and fact-checking. He'll reply to the thread if any part of this statement is not true.)
Sometimes the secret BCC is made overt by an explicit CC. In this case, the person is announcing to the thread, "See, I CC'd Raymond and he didn't say anything, so therefore I am right and you are wrong."
Another variation on the BCC trick is to send a question to a discussion group and secretly BCC me (or overtly CC me) in order to say, "I'm asking the discussion group for help, or maybe Raymond can answer it." Or even worse, "I'm using Algorithm X, and maybe the discussion group can tell me whether it's the correct algorithm. (And even if they can't decide one way or another, then certainly Raymond will tell me if I'm doing it wrong!)"