People also have different ideas of what "hard" is. I've never tried setting up a mail server so I'm talking out of my ass a bit, but after reading the article it sounds like you'd need to do a bit of googling/trial and error changes to get things set up, probably one of those projects that would take up most of a saturday or at least a saturday afternoon and might run into some hiccups every few months that requires more googling/tweaking.

Even if I'm way off base about the mail server set up being this way, some people still consider this type of "saturday afternoon" project hard compared to something that just works out of the box without any fiddling and can be set up in 20 minutes. I'm not trying to be elitist by suggesting these people are dumb or lazy, just that the semantics of what "hard" is varies for people, especially with little projects that require fiddling/tweaking/looking for outside help.