Ok, Kev asked me to chime in here, but before I get started let's have a quick sanity check:
Moderators can delete any post at any time at their own discretion. Moderators are expected to exercise discretion when doing so, but ultimately the choice and the responsibility is theirs. Your flag does not place any additional responsibility upon the responding moderator's shoulders, nor give him a mandate to do something he otherwise would not. He alone will answer for his actions, and therefore if he does not feel an action is justified he has the ability and indeed the duty to decline the flag requesting it.
When flagging, your success rate is determined by your ability to clearly communicate what action should be taken and why. Most of the time, the work is pretty much already done - a question is visibly non-constructive, an answer is obviously not an answer, and you need only pick the flag option that corresponds to this. Sometimes, more explanation is needed.
>>>>>>>>>>>>>>>>>end of sanity (check)
So let's talk about "not an answer":
This was posted as an answer, but it does not answer the question. It should possibly be an edit, a comment, another question, or deleted altogether.
For a moderator, this presents one of four action items:
- Convert to an edit (if posted by the OP)
- Convert to a comment (if intended to address some issue with another post)
Which one of these is appropriate should be obvious from the context:
- Clarifications and additions to the question should be converted to edits.
- Useful commentary on other posts should be converted to comments. This includes answers that ask the OP for additional information, etc.
- Follow-up questions, "I too have this problem", off-topic / non-constructive commentary directed at other posts or their authors, and random bits of noise and fluff that make no effort to answer the question should be deleted.
- Things that are legitimately answering the question (even if incorrect) should be ignored.
This is pretty visibly not an answer. It's also not an edit, and not a useful comment. So the remaining action is ol' #3, delete. Moderators can and do make these decisions very quickly - there are a lot of non-answers posted and flagged.
And then there are link-only answers
I'm not going to re-hash all of the problems with them, from spam to broken links - we're all plenty familiar with the pain they cause. But here's the thing: sometimes, they do answer the question - because it's a bad question, or because it's just a really useful link. The problems remain, but strictly-speaking 'not an answer' no longer applies.
Of course, the best outcome for a useful link-only answer isn't deletion in any case - it's editing! If someone, particularly the author, comes back and expands that link into something that directly addresses the problem and uses the link as a reference... Now you have an answered question without the problems of bare links.
Straight-up deletion is problematic when the link is actually useful - at best, you're encouraging someone else to re-post it with more of an introduction; at worst, you're turning an answered question into an unanswered question for the sake of Purity.
And converting them to comments is really sort of an abuse of comments. Most not-an-answers make lousy, worthless comments too - spam in a comment isn't a whole lot better than spam in an answer. And for those useful link-only answers, you're just turning something that could be improved (anyone can suggest a fix for a broken link in an answer) into a disposable "Post-It note" that can't ever be fixed and will probably just end up deleted. I've seen questions, sitting around for months or years, nominally unanswered but in reality answered by comments... Congratulations, you've recreated a worse PHPBB within Stack Overflow.
I should also note that we've been improving the filter right along to block more and more link-only answers before they're even posted - this too is preferable to deletion, since the author can easily expand the answer and re-post. Of course, it does nothing for older answers. We're also working on tools to fix broken links. In answers...
So what's a mod to do?
In most cases, a link-only answer is just going to be deleted. Let's face it: the moderators on Stack Overflow really don't have time to be doing in-depth analysis on the benefits of a flagged answer that looks lazy. But to avoid the problems I outline above, I've recommended a bit of caution in the past:
as a sanity-check next time: no matter how lazy an answer is, if there isn't a better (objectively more detailed, comprehensive, or - this is key - useful to the asker) answer, deleting it / converting it doesn't really accomplish anything. Its acceptance may indeed indicate the question itself isn't very good, but if so you should focus on the question.
In the particular instance you cite, the question itself wasn't a good question; indeed, it was a shopping question. Link-only answers are common on shopping questions - unless you can preserve other, more educational answers by cleaning them up, it makes more sense to just close and/or delete the question. This has now been done. Fixating on the answer here (which was +10 and accepted, but since it was posted by the asker acceptance doesn't mean a lot) means not seeing the forest for the trees.
But even decent questions sometimes get link-only answers, and if there's only one useful answer, deleting it to achieve purity accomplishes nothing.
Remember: moderators are doing this quickly - snap decisions to delete, convert, or leave it be. There may be some complicated reason why a lone, up-voted, accepted answer should be removed, but chances are the moderator just sees a lone, up-voted, accepted answer. Which brings me to...
So what should I do?
There's a lot you can do, actually...
If you're familiar with the subject, you can make a quick edit: quote or paraphrase the relevant portion of the article, copy and attribute the relevant bit of code, or even just write a small introductory paragraph.
Leave a comment for the author, asking him to expand his answer a bit. Link to that FAQ... Maybe throw in a down-vote.
Vote to close and/or flag the question if a poor question is leading to poor answers.
Flag as "not an answer"
If the answer looks like it's been useful, but really just needs to go, flag with a custom reason and explain briefly why:
"Cleaning up poor answers to borderline question so the good ones can remain"
"Link is broken and cannot be fixed"
"Link contained a live bobcat"