I'm having a hard time understanding the reasoning behind closing questions. Not that I think questions shouldn't be closed, but I do not understand the reasoning and/or thought processes behind closing questions, ...
The Super User FAQ goes into wide detail on the reasoning behind closing questions; most of the questions you have linked are subjective in a bad way, you can find more detail about that here.
..., and what it is we hope to accomplish by doing so.
The Stack Exchange network can be summarized with the word learning, more specifically learning to solve actual practical problems; if a question only yields opinionated answers with argumentative comments, then there isn't any benefit to keeping the question open or keeping it around. You don't learn anything from people solely trying to prove each other wrong.
Obvious things like shopping recommendations we just plain don't want here. But what about things like this?
- Is the performance of a CPU affected as it ages?
While the question and top answer look fine, if you look beyond that you see people coming up with answers that tell the opposite or are somewhat irrelevant to the question; for instance, perceived speed is mentioned as well. There's also quite some arguing in the comments.
- How are commercial DVD's burned? (...)
Not subjective, but might be somewhat off-topic if you see our site is mostly about computers in a home setting. Although there's no other site for this question nor is it in any way bad, I have voted to reopen this one.
- What is the origin of K = 1024? (Good question, bad answers?)
Been there, done that on a similar question.
- What are the pros and cons of a solid-state drive?
Pros and cons are somewhat subjective, this invites discussion of how much something is a pro or a con and doesn't give a definitive answer. A simple understanding of what a SSD is, how it works and what implications it has; is what makes people ask such question. Figuring out the main pro (more speed) and con (less space) probably is easy and makes sense, pros and cons beyond the obvious ones are more likely open to debate. Take for instance Moab's comment "Biggest con is data recovery" — but what if someone then comes up with "Biggest pro is that it's less breakable"? Which one of both makes sense?
- How to run Mac OS X within Windows Virtual PC?
Are "Hackintosh" questions allowed?
- How can I gently explain to non-techie friends they are the victim of a hoax? (...)
My comment would be "Just tell it to him." as not being able to express yourself is not a SU problem.
- If spaces in filenames are possible, why do some of us still avoid using them? (...)
There are a ton of reasons, but a definitive answer, no. Questions that poll for a list of reasons are equivalent to research that you could do elsewhere, Super User is not a place to do a study on why people do things but rather a place to solve problems. It's like the typical "spaces VS tabs" and "best IDE" debates, all subjective. Gathering such reasoning can help obtain slightly more objective statistics (resulting in facts) to look at, but the Stack Exchange system doesn't support a large number of answers and probably never will change that way.
I'm also a little confused about locking vs closing vs deleting. It seems locking or deleting are rarely considered. Many of the above questions would make more sense to me if they were simply locked.
Locking is mainly to avoid people from editing stuff, when multiple persons disagree with the content of a certain post. Or when people keep editing something into a post despite it having been rolled back a few times.
As for deleting; what you don't see, you don't see. There has been deleted a lot over time.
- What do we hope to accomplish by closing questions?
Keep the site clean of content that defer people from giving an "actual answer" to a useful question.
Stack Exchange is no place for discussion, apart from the meta sites where we can discuss about the parent sites.
Some questions have valuable information to retain, so we keep them to keep them accessible.
It's also no teach the users what kind of questions we want and don't want, as they come across them.
- How does this help the site?
It keeps the site at an expert level, making it stand apart, it's what makes up its success.
Again, not trying to play Devil's Advocate or whine about questions being closed. I honestly do not understand the intent of closing a question.
Let's hope you do have an idea now; if still unclear, stay around for a while and it'll probably make more sense with time. Remember that we're trying to stand apart from a typical support forum... :)