Why can't I tell who moved this question?
Since the security.se site is not one of the 'Top 4' it does not appear on the close to vote migrate page. As such, it requires a mod's intervention to migrate, and that is what happened in this case. If you want to see the closed question on the SF site, then per this meta-SO answer, you can append a
?noredirect=1 to the URL.
I will admit that I had flagged that question for migration to security.se. Reading the question, the prospect of a virus infection on the site's DHCP server is pretty scary, and working under that assumption, the Information Security community could provide some excellent assistance. Is it possible that I flagged in error? Sure, that's always a possibility. Though I take some comfort in knowing that I wasn't alone in that opinion, or else it would not have been moved.
if there are going to by superspecialized sites like this is serverfault essentially dead?
I wouldn't necessarily agree with that. Having not read the faqs on most of the other speciality sites I can't get overly specific. However, glancing through the unix.se faq, I do see that there is definitely some overlap between what they say is on-topic and what goes on at SF. I also see some some major differences as well. I am nervous about fragmentation, look what this did to the linux community in the late 90s and early-mid 2000s. We will have to wait for those sites to get bigger before we really start to see what the fallout might be or whether those fears are justified.
In the end, the whole point of having the different communities is to encourage an environment where certain kinds of questions can get good attention. Migrations definitely help with that, but as always they really need to be focused on one thing -- Where can the asker get the best input?