Oldie, but goodie, yes. Twitter is a bit heavy and permanent for the informal back-and-forth in the IRC chat rooms.
While I would take a dev's Twitter post as gospel, i.e. solid commitment, I take IRC chat as a much lower level of commitment and do not copy/paste IRC chat since it's usually more off-the-cuff.
Another nice benefit of IRC chat is other people besides the dev can answer questions, which helps to offload the dev. And, not everyone is in IRC chat, so it acts as a filter. I have yet to see a troll / flamer in IRC chat, though I'm sure they exist.