I think that questions of the form "I've seen X happen in anime. Does this happen in real life in Japan?" aren't really questions about anime (usually). They're questions about Japan. There are exceptions to this, like when X itself is an anime-related topic. For example, asking a specific question about how realistic the portrayal of the anime production company in episode 8 of OreImo would be acceptable (I can't think of any questions regarding this at the moment, but it would at least constitute an acceptable topic).
However, if the same question could be asked without making any reference to an anime, and the answers would be the same, then it's not really an anime question. The linked question "Is it common for Japanese bars to require advance reservations?" is probably an example of that. Hence, I propose the following policy:
Culture questions need to be directly related to anime/manga. If a question about Japanese culture still makes sense removing all references to anime/manga, then it's off topic.
These questions might make sense on Travel.SE or JLU.SE, but they aren't squarely within the expertise of anime-fans. For those interested in such things, the Culture and life in Japan proposal on Area51 would include a lot more questions like this. Some of these questions might still get answers here, since most knowledgeable anime fans also know a lot about Japanese culture, but it isn't strictly a question about anime.
Some of these questions might still be able to converted into valid questions, though often not culture questions. If X is something that happens quite frequently in anime, though it seems to be less common in real life, then asking about the origin or meaning probably makes a valid tropes or symbolism question. An example of this would be Why is "I won't forgive you" a commonly used threat?Why is "I won't forgive you" a commonly used threat?. Some of these questions will get answers of the form "Actually, this is common in real life in Japan, not just in anime". However, just asking whether it occurs in Japan is off-topic. Also, note that such questions typically need multiple examples to be reasonable. Depending on the trope, it may require more or less, but IMO three examples is a bare minimum.
As a note, strictly speaking, the tag culture is misused pretty frequently. It's not for questions about Japanese culture broadly. Those are off-topic. From the tag wiki, it's for:
Questions about anime and manga in the broader context of Japanese culture. Includes both questions about cultural origins for anime/manga references and questions about the cultural impact of a particular series.
Some examples of culture questions which are properly tagged are What factors contributed to the "golden age" of anime?What factors contributed to the "golden age" of anime? and Why does censorship level differ between manga and anime?Why does censorship level differ between manga and anime?. It doesn't include arbitrary questions about Japanese culture, nor does it include questions about tropes (unless the explanation is certain to be based on Japanese culture).