I mean, I can give you the reasons that I have a hipchat account which I use with my coworkers, even though a good 50% of us are also on IRC for other purposes.
1) It proved to be a pain supporting the non-techies using IRC
2) Nobody wanted to maintain the IRC server and set up logging. (And, if you add up the couple hours to do so and maintain it in a year, hipchat ends up being a good deal)
3) Some of our people use the SMS and xmpp integration, which makes it easily fit into their existing communications.
4) The API, web based search, gui admin, github integration, unfuddle integration, etc are already setup and/or written (an extension of #2)
5) Nice handling of large chunks of pasted text. (The web and desktop clients format them in fixed width properly and limit the size but provide and expand link.) This is more convenient than pasting a pastebin link, and works better than irc because of line breaks.
I mean, basic economics as well. If someone spends an hour a year maintaining the IRC server, helping non-tech people get onto IRC, etc, then paying for hipchat instead, for 4-8 people is well worth it each year.
(This is all after having used a channel on a public irc server, then someone set up IRC on a vps, then we used grove , and ended up on hipchat for the past year.)
