Earlier quoted context omitted.
I hear what you're saying, but, come on! apt-get install ejabberd 5 minutes of conf file tweaking and you're done. Seriously that's it! I did this about 8 years ago and haven't touched my setup since. There's pretty much zero maintenance to do with an XMPP server.
What happens when ec2 shuts down the machine with jabber on it? When there's a memory spike in the middle of your vacation and no-one can send messages? Etc, etc, etc
What do you do when hipchat's severs are down? Twiddle your thumbs and wait for it to magically come back? At least if it's your server you can actively fix it instead of waiting for someone else to do it…