MO is for research level questions: i.e., questions that graduate students or post-PhD mathematicians encounter in the course of their research, or those of equivalent level and content. But no matter how I looked at the question, I couldn't see it as research level. First, the question as it has been asked seems to be based on the assumption that cardinal numbers have reciprocals (which are also cardinal numbers). But this is a profound misunderstanding of a kind that a professional mathematician or student of mathematics would not make. Second, Professor Borcherds has pointed out that there is some number system in which it makes sense to take such reciprocals: the surreal numbers. That's an insightful remark, but did the OP have this in mind? If s/he had expressed problems with .9999999... = 1, then would we answer the question by reference to non-standard analysis?

For me, the clincher here is this: suppose the question does refer to the surreal numbers. I personally know next to nothing about this topic, but I am told (by wikipedia) that they form an ordered Field (the capital letter is hinting that they are a proper class, not a set). But of course I know that in any ordered field, if 0 < x < y, then 0 < 1/y < 1/x. In other words, even charitably interpreting the question in a domain where it makes sense, the answer is immediate.

If anyone can explain to me why there's more to the question than this, I will be happy to vote to reopen.

That said, when a question is "so elementary or so wrong" then there surely are other reasons to close the question. In this case, the question should be closed for those reasons. It is perfectly fine to comment on a closed question. I find that the best comments indicate how to ask a better question, but answering a closed question in a comment is not necessarily bad behavior.

One thing to keep in mind is that we all want to encourage people to ask good questions on MO. Comments and votes to close are best used to steer users (especially new users) in the right direction. In this particular case, the right direction might be math.SE, but I'm not sure about that and nobody has suggested that in a comment.

François: Having an answer in a comment has never been a valid reason to close.

This is something that I feel needs clarification, because it is not an uncommon situation. My attitude is that if the question is so elementary or so wrong that a short comment suffices to completely answer it then it would be appropriate to close the question. In other words, frequently the reason why the question was answered in a comment may is that the question is inappropriate for MO, with the act of answering in a comment serving as evidence. Sometimes, transferring the comment to an answer leads to a quick resolution (the OP simply accepts the answer and the question goes away); sometimes the OP is not mathematically qualified to understand the answer or even to formulate the question properly, which leads to unproductive discussions of little benefit to anyone else. If the OP is satisfied with the response and the respondent does not wish to repost his or her comment as an answer, I usually vote to close as no longer relevant.

Robin: "Is there any reseatch [sic] on this?" seems like a legitimate reference request to me.

Ryan: Yes, Richard Borcherds gave the best answer I can think of. Having an answer in a comment has never been a valid reason to close. I also don't agree with your wikipedia test: what could the OP have looked for to land on that page? [Edit: Ryan and Mariano have given very good answers to this question.]

As a moderator, my vote to reopen the question would automatically reopen the question. This is a boundary case where I wouldn't do that without community support, so I'm starting this discussion to poll the community. You may consider this to be a single vote to reopen.