I just noticed that the Batman question was closed this past February, which seems a sad fate to befall such a historic and beloved question on this site. I understand there were always concerns about the quality of the question, particularly the research effort, but it was pointed out in the comments that simply plotting the equation may not have been as straightforwards as it looked, indicating that there was value in having the question on the site for the benefit of those who do not have the skill to verify the authenticity of the equation for themselves. At any rate, it certainly didn't seem bad enough to warrant closure.
I also don't see how the question could possibly be off-topic - it is a clearly-defined and well-motivated question which can be answered unambiguously. Is it simply the inordinate amount of attention the question received? Even if it always received a ridiculous number of upvotes (I'll admit I provided one of them), it had been around for a long time already; the attention had mostly tapered out and it really hasn't been visible on Math.SE for a long time except where you looked for it (by going to the most upvoted questions page). Even if that were the case, it seems that protection would be more appropriate. Was protection not sufficient?
It should also be noted that the suggestion of closing the Batman question was brought up before and negatively received (albeit a long time ago), so something has changed. Is this just another case of Math.SE getting crankier over time?