The step to remove us from the SO migration targets wasn't asked for by 'us' lightly, nor was it given lightly - @shog9 looked into this for some time before agreeing that it was the right thing to do. See this SF.Meta question to get an idea of how the decision was arrived at.
Professional sysadmin questions are welcome on Server Fault. We make no distinction between people who are new to the job and people who have been doing it for so long they can remember when Unix was a strange new idea.
Where we are strict is in the standard of the questions we expect people to ask - we dislike "Hai! I can haz server spec for mai youtube clone?" questions as much as SO dislikes "Gimmie teh codez", and we are strict about enforcing that; possibly overly so where it impacts new sysadmins, true enough :-( but that doesn't mean they're unwelcome.
Taken from our FAQ:
Frequently Asked Questions
What kind of questions can I ask here?
Server Fault is for Information Technology Professionals needing expert answers related
to managing computer systems in a professional capacity.
To a greater or lesser degree, that's been the mission of SF for about as long as I can remember, and where it hasn't always been applied consitently in the past we've lost a number of high rep site members who have become fed up with a stream of low-quality questions.
To give you an example from SO.meta of the sort of questions we have to deal with (directly as well as migrated in the past, I hasten to add), look at the "free hosting" question. Sadly, a lot of people who frequent SO have migrated questions of the level being discussed there to SF in the past.
The problem isn't all of you, the minority who participate in meta discussions and see the discussions about "don't migrate crap" and "pay attention to what you're doing in the review queue", but the majority who have enough rep to participate in SO but who don't really join in with the community.