Not entirely. Team control is a major part of it for companies, and history makes a huge difference to the experience. Slack servers allow the use of IRC clients, but I gave up on Colloquy almost immediately after seeing the benefits of history. For the right teams, the IRC+history combo can almost completely eliminate email use.

Also, Slack bought a company which did voice, video, and screen sharing. Since join.me went downhill, this will be a welcome addition to Slack.