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Why do you cast downvotes on answers?

Coming to the site, it seemed that downvotes are obvious for questions that are wildly off-topic or simply a mess (no effort in writing, badly written, unclear question, pretentious assumptions, clear misunderstanding of anything and everything ever conceived).

However, I've been seeing a lot of downvotes recently for questions that are either on-topic (specifically about the subject matter of the site) and clearly not a mess (written well, with effort, humble tome, slightly unclear question).

Are there any reasons for downvoting a question that I'm not seeing? Or should I take these as anomalies?

EDIT: I'm speaking of the Trilogy sites.

EDIT2: Yes, I do expect the downvotes of irony that this question will receive =(

Some examples of downvotes for on-topic questions:

• How can I wait for a file to be uploaded via ftp then delete it? -- A fully on-topic answer, albeit slightly badly written. Yet, I was able to understand it completely, and it has a very real answer. Surely, editing for clarity is the proper course of action here.
• What is the point of the anti-cross-domain policy? -- Well written, fully thought out, asker provides his own attempts at figuring out his problem
• How do Clojure programs/compulers/interpreters actually "work"? -- My own selfish example that may or may not have been the inspiration for this post >.>