@YemonChoi: I agree that MO neither is nor should be a common place to ask for feedback on preprints -- but I would not be dogmatic here. Rather I suggest to make further actions (closing/removing the post or responding, etc.) depend on the quality of the material in question.

Unless a duplicate asks the same question in a substantially different way, I think in the present situation deletion is probably the way to go -- otherwise one would open the doors for plagiarism.

I agree to what you write -- but what is the purpose of your post? -- Finding enough people to convince SE to allow again closing questions as duplicates of unanswered questions?

Well -- I think on the one hand, such a question could be seen as a place where to advertise particular products. On the other, I guess many people will be reluctant to recommend particular products, since doing so may be mistaken as spamming.

I think the question was probably just closed by mistake.

@ToddTrimble: Yes, my proposal is to leave this as it is, i.e. the question-downvoter looses no points. I think taking away points from the downvoter would be almost a similarly bad idea as giving points to the upvoter -- both would effectively prevent an unbiased decision. Further, to be precise, I'd suggest to make gain / loss of points independent of the order in which the up- and downvotes on a post are cast, i.e. $+5/-5$ is always zero, as is $+3/-10$.

@Todd: Would it reduce your concerns if voting would be symmetric ("loss" from a downvote equals "gain" from an upvote), but there is a cap at zero, i.e. no post may result in total in a loss of points?

I'd say whether a question should be kept or deleted depends on whether it has still positive value for readers or not. If you think the latter is the case here, deletion shouldn't be too much of a hassle.

Actual deletion either requires the question to be closed (needs 5 votes) and then a number of delete votes depending on how many answers with what vote scores the question has, or moderator intervention.