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.
Do you get file sharing, easy group chat, @mentions across rooms, public temporary invites to customers into internal channels, very easy github and zendesk integration and, the killer feature for me, a searchable archive over all conversations?
I'm sure you can do all of these with ejabberd and some additional external tools, but setting all these components up goes way beyond just apt-get'ing the software.
Now, you might not need some (or all) of the additional features, so ejabberd is the perfect solution for you, but you can't jump to the conclusion that because you don't need a feature, nobody does.
I'm a quite new HipChat customer - we were using skype before, but the indexed archive is a total killer feature for me and already helped me and my coworkers a lot as it helps us to learn from conversations between other people, thus reducing the amount of stuff that has to be asked multiple times.
For me, that's totally worth the $2 per user per month.
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
You turn the machine back on? Switch to a server provider that doesn't randomly shut your machines down?
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…
