Previously my understanding of CW was hazy; I had thought of the designation as being primarily for subjective topics, e.g., "What's your favorite "programmer ignorance" pet peeve?"
This is only partly true. If you ask a subjective question, then yes: it should be community wiki. But it's important to clarify that community wiki does not make subjective questions okay. You should not ask most of your subjective questions in the first place.
Additionally, sometimes we will have questions that are related specifically to the field of programming in a way that is not relevant to other career fields, but not to the activity of programming. These questions might be still a good fit for the site or they might not; that's the nature of the community driven filter on whether a question should be closed. Probably most of them get closed, but a few of the better ones might deserve to remain open. However, regardless of whether or not they stay open they are generally non-technical questions. Often they are subjective as well. I think this pretty well describes the question you linked to.
On Stack Overflow, we generally prefer that users only gain reputation for posting technical content (this is likely true of SuperUser and ServerFault as well, but perhaps not other Stack Exchange sites). Therefore, we ask that these questions be marked CW to take advantage of a side-effect of the community wiki flag, so that the non-technical posts will not earn reputation for users.
Again, it's important to mention that CW is not a free pass for the question. It makes no more or less likely to be closed. Additionally, it's not a good idea to point at older questions as examples of something that was left open or not marked CW. Standards have evolved over time and the ability of a question to find an audience depends on who is active on the site at the time it's asked.