Warning: wall of text ahead.
As I stated before, I don't downvote topics because I don't find them useful. I downvote if something is clearly idiotic or factually wrong or someone's being a jerk--which I don't think I've seen yet. Writing is so broad, it seems to me that these basic criteria are the only sensible ones. By contrast, the normal StackExchange criteria is the idea of usefulness, but aside from using words, fiction and non-fiction don't have much in common. I suspect there are more fiction writers (or aspiring fiction writers) here than there are technical writers. If they downvote technical or non-fiction questions, this is discouraging to the non-fiction crowd, and they're apt to leave. This seems to be an obvious unintended consequence of the "usefulness" metric.
Another concern I have right now is a cult-of-personality problem that seems to be developing. Dori's posts tend to get downvotes, but I suspect this is less because of the content, and more because of who posted it. (Example.) If this is indeed the case, this behavior needs to be thoroughly slapped down because it is completely and utterly counterproductive, but unlike Slashdot, StackExchange doesn't do meta-moderation AFAICT.
In terms of non-fiction content... like I said above, aside from using words to communicate, fiction and non-fiction usually have very little in common. For a "creative" discipline, technical writing isn't very creative. Generally speaking, you're condensing an idea or some piece of knowledge down into actionable steps or set of easily digestible bits, depending on your audience, and what you're writing.
As such, we non-fiction types don't really run into the same problems that fiction writers do. With some basic caveats, I don't need to worry about, say, word choice in the way that a fiction writer does when they're trying to create a setting or mood in their work where a poorly-chosen word can ruin a whole paragraph.
Along similar lines: a lot of technical writers do it for a living. It's not a hobby. That means they're doing it 8-10 hours a day, 5 days a week, 48-50 weeks out of the year. Assuming more conservative numbers: 6 hours a day, 5 days a week, 48 weeks a year gives you 1440 hours a year or writing. If you take Gladwell's 10,000 hour figure seriously, it'll take you 7 years to be a master. I suspect a lot of technical writers here have more than 10,000 hours writing. In some cases (not me), A LOT more. As such, we probably don't have as many questions to ask, simply because we've "paid our dues" already.
On the other hand, fiction tends to be a hobby, therefore you probably find more beginners doing it (first 1-2,000 hours) than you do veterans because they don't spend their days doing it. You wouldn't expect Stephen King, for example, to have many questions, or Neil Gaiman, but I have no doubt that there are some technical writers here who have spent more time stringing words together than both of those authors have, so they probably don't have much left to ask.
That leaves the teaching component. I'm not good at it. It's that simple. My best advice on writing is to "Just do it" and then I'll help edit later, and explain why the content maybe needs to be edited if my corrections are not obvious, but I'm not very good at contriving teachable nuggets where I could propose a question, wait a day, and give a possibly-ideal answer.
That being said, there are clearly developers and other technical people who are working on improving their communications chops, and I thoroughly enjoy helping those people, and while I know Writers.SE is still finding its niche, I suspect that's the kind of non-fiction writing you're most likely to see for the foreseeable future. :)