1. Tinfoil hat time! "Pisshorse" make money off of hosting their own software. So they are financially incentivized to make it as difficult as possible to install yourself, but at the same time they get to go "woooo, open source" as much as they like.
I'm convinced Oracle did the same sort of thing by making their DB product impossible for normal people to understand, in order to charge outrageously expensive consulting fees to companies. Or so I hear; I've never used it so I could be wrong.
2. Your users aren't always who you think they are. I learned this one switching from back-end/n-tier work over to front-end CMS based web dev. Yes, the users are the people browsing the website, but the users are also the people trying to use the damn CMS, so the website UX and design extends to those people as well.
Meaning, instead of forcing your hapless marketers to use some crazy admin panel with thousands of options and checkboxes, or even try and edit XML configuration (I've actually seen this), any time one extends the functionality of a CMS, creating some custom front-end UI to control it is a basic necessity.
In the same vein, any sort of software (and hardware! printers, tools, cars, whatever) has to consider the installation and maintenance of itself as a UX/design concern and the fact that it has multiple domains of users.