I've had a problem with this ever since it was posted, but NickT's discussion on the interpretation of the "practical/answerable problems" clause in the FAQ sorta/kinda helped me put into perspective why.
Story, trivia, and terminology-type questions are on-topic for the site. The issue with this type of question (as expressed in the answer I disagree with here) is that it's not practical - but knowing the explanation behind a story element or trivia or terminology question is often similarly impractical.
Knowing what Ryu says when he delivers a flaming uppercut isn't practical, (the game plays the same even if you think he's saying I WANT A HOT DOG) but the community seems happy with such a question.
Take "the cake is a lie" - this is a meme that grew out of Portal, and it's specifically referenced here. This is popular and obvious, but it's also tangentially related to the story of Portal. Someone could legitimately ask what this means in the context of the game. It's as practical as any story-related question, and it's certainly answerable.
Practical and problem to me are somewhat interchangeable in the previous section. Let's demonstrate:
The issue with this type of question (as expressed in the answer I disagree with here) is that it's not a problem - but knowing the explanation behind a story element or trivia or terminology question is often similarly not a problem.
Knowing what Ryu says when he delivers a flaming uppercut isn't a problem, (the game plays the same even if you think he's saying I WANT A HOT DOG) but the community seems happy with such a question.
The point I'm trying to make is that sorting story/plot/trivia/terminology questions based on whether or not they're funny or popular does nothing to change whether they are practical OR problems. If funny or popular story/terminology/trivia elements are not practical or not problems, then we should say the same about all classes of those questions.
Mark's answer on NickT's question I linked above gives some additional detail, and it's a good read for understanding this particular part of the FAQ.
Knowing The Meme
At other times, the objection appears to be that they are popular, obvious, and (in some cases) only tangentially related to gaming.
Returning to our previous "cake is a lie" example, there are a lot of sources on the internet for the meaning of this particular phrase, and it's relation to the game. This means that the question potentially shows little research effort - the response to this is downvoting and not closing. Saying "there are other sites for this topic" on the internet is also a bad argument - if that were a reason for closure, we'd have to close quite a few Skyrim questions with a pointer to the UESP or the Skyrim Wikia. They often have more detailed diagrams, tables, and charts on various subjects than we can hope to produce independently.
It's also possible to ask a non-gaming related question about a meme/joke, but it's also possible to ask non-gaming related questions on just about any topic, so I don't believe that is a reason to ban the entire class of questions.
WHAT IS A MEME? A TWISTED PILE OF OBVIOUS SECRETS!
The other thing I have a problem with is that categorizing a story, trivia, or terminology question as a "meme" (and therefore deserving of closure) simply means that it is popular currently. This is a problematic way to categorize what is good or bad.
At a high level, if something gaming-related is getting attention outside the gaming community, we want to discourage questions about it? Why limit our audience in this fashion?
Who is deciding when something is popular enough that a question about it should be closed? Do we have some metric of internet popularity we are going by? Should I be checking trending hashtags on Twitter before I post, just in case?
Let's take the "current popularity" aspect to the extreme - say I asked a question about a specific part of a game that was weird or new or interesting. In a week, it's exploded on the internet and KnowYourMeme has a video dedicated to it. Do we retroactively close this question as being a meme?
Take the reverse case - say 10 years from now we're all playing Final Fantasy Hojillion-2 or whatever, and in there is a hidden room that's full of cake, and an NPC is telling you that "it's all a lie." Someone asks about this hidden room, and wonders why "the cake is a lie" is supposed to be a fun easter egg. It's been years since that was a meme, but it was a meme at one point. Should we close a question about a former meme? (For an example of this, see this question about a reference to Sherlock Holmes in TF2)
It's possible to ask bad or off topic questions about memes or gaming "in-jokes" - but it's possible to ask bad questions on almost any topic. Taking different action on these questions than any other story/trivia/terminology question is problematic and counterproductive.