Why some questions are written in this funny way?
My impression is that the phrase was written by a non-native speaker of English, who does not know how to construct questions. (How often that impression is accurate I don’t know.) All of the examples you offer are noun phrases. For example, “why we need SELinux” might serve on its own (sans question mark) as a headline, or as part of a complete sentence:
- Tell me why we need SELinux.
- Why we need SELinux is…
But the terms may not stand on their own. English questions use inversion of word order and auxiliary verbs; noun phrases involving question words do not:
- *Why Paul went to the concert?
- Why did Paul go to the concert?
- Paul went to the concert.
The people writing these question titles are using (1) when they should be using (2), because it more closely mirrors the structure in the declarative version, (3).
Now, “Why turn ‘collate’ off?” is incidentally valid. It poses a rhetorical question using the bare form of the verb (in this case turn), asking essentially “why would you ever bother turning the ‘collate’ function off?”—why here is standing for why ever. Common examples:
- Why bother?
- Why wait?
- Why waste your time?
- Why not?
The style of these titles is that of an indirect question. What is missing here is an introductory phrase, such as "Now we're going to discuss why we need..." and it looks like the introductory phrase has been left out. Some introductory phrases are direct questions, such as "Do you know why we need...?", so when you leave them out what remains is the indirect question with a question mark which belongs to a phrase omitted. Personally, I believe that the latter is not nice stylistically. But when there is no question mark at the end, titles of this style don't strike me as odd.
“Why ATM and MPLS are at level 2.5” and “Why Turn Collate Off” are perfectly grammatical titles (the second fragment is even title-cased). They are not questions, and do not pretend to be questions.
“Why we need SELinux” and “Why BitTorrent uploads simultaneously” would be perfectly grammatical titles; they are marred by a spurious question mark. I suspect the presence of the question mark has something to do with the context: they are titles of questions on Stack Exchange, and the environment provides contradictory clues — when you type a title, the label next to the box is “Title”, but the guide that appears inside the box is “what's your [topic] question? be specific.” The pressure to write something that is both a title and a question often results in a title that's superficially made more question-like with the addition of a question mark.
I don't like “Why the letters in keyboards are arranged like this?” with or without the question mark. I'd prefer “Reason for the arrangement of letters on keyboards” or “Why the letters on keyboards arranged the way they are” or “Why QWERTY…”.