> If someone is asking then either they failed to find the "duplicate" based on their search terms, or their problem is subtly different and the other answer doesn't help, or they don't understand the other answer.

Or they didn't bother searching possibly?

I think the 'up-vote only' model might be helpful for SO. If 1000 people down vote, but 100 people up vote, who's vote should carry more weight? Obviously, 100 people found the question/answer useful, so it's not useless. Whereas, we don't get a lot of value from a down vote, just that each individual that down voted didn't find the information useful/relevant.

If it's indeed a duplicate, well maybe it is, but perhaps the new question is a better version of the question (more/less generic/specific depending on context).