I know many people operate this way, but it's not standard enough. I get people who CC me on stuff because they want the primary person to feel like they're the real decision maker, and the CCed people are supposed to chime in if we want to support or vote down the email's content. Who is CCed and who is TOed can be something of a political game. Not saying it should, but it is.
I've fought back against this very thing (and was fairly successful with the results). It required a lot of force and careful wording.
"No, you didn't send anything _to_ me. You did copy me a message you sent to someone else, however."
I went out of my way to filter all emails CC'ed to me to another folder called review, and I would review it at the end of the day, or maybe the next day. It took a lot of standing ground and being blunt with people, but eventually it started to work. Before I left, there was discussion on improving email communication, and making it clear to everyone in the company the difference between CC and TO, and how to use them, when to use them, and what to expect.
I'd hate to think what I'd say if I was in the middle of your situation. I don't play the political game well. =)
