It seems to me that "Not Constructive" is being overused...
I was thinking about this after having a question of mine closed:
What are the benefits of "enterprise-level" virtualization?
And now this one has shown up in the Review Queue with a couple NC votes:
What are the merits of SAS vs SATA drives?
Obviously I think the first one is fine, but then I specifically ran it by people in Chat first, and you can see the results in the voting on the Q and the As. The other question is even more highly voted (admittedly, there was more voting back in 2009).
To me, both of these are Good Subjective:
They aren't shopping questions. Shopping questions ("What product/service can do this?") invite a long list of possible solutions. Both of these questions are scoped so that there are only going to be a few possible answers.
Although they call for qualitative answers, they aren't asking for opinions, they're asking for facts that can be backed up. e.g. for the virtualization question, the answer that enterprise-level products have better support is a fact, not just an opinion.
I think these types of question are something that can make SF more appealing to and more useful for experienced sysadmins. They're useful questions to have on the site and they're good opportunities for people to share some of their experience. Instead of closing them because they're structured a bit like shopping questions, people should at least leave them open and preferably upvote the answers.