I can't answer for every moderator, and the closest thing I found to an official policy is this question on meta.SE, but I can tell you my perspective.
In the case you describe, where a user has written a new answer that isn't the exact same text as an old one but has the same information, typically I'll leave a comment telling the new user that their ...
Yes, it is.
Especially with the examples quoted, all the more so. Older question is not clear and OP didn't revise to make it clear. Only answer to that is based on a supposition of OP's intent. Newer question is clear in intent and has a detailed answer (with a bounty awarded )
Marking the older question duplicate of the newer one would benefit those who ...
In this case I think you should feel free to ask a separate question since the devices obviously have different features for this. Bonus points if you link to the existing question and mention why you're asking the new one.
Your question says:
There is already a similar question to this one, but mine is narrower in scope
Yours is much more detailed, but I don't see how it's narrower in scope. Your question says:
Can I prevent such an app from running in the background?
The other question says:
Is there a way to prevent the service apps (or any other apps) from ...
I just want to add to Matthew's answer that I think that the confusion comes with the fact that it's hard for the average user to distinguish between an Activity and a Service running in background. We have two questions
How can I stop a Service from running in background?
How can I stop a App from running in background?
Both a very similar. Yet there are ...
The project is drawing to a close, and I am planning to take down the annotation interface this weekend.
Thank you very much to everyone who helped out, and thank you for all the valuable feedback and suggestions. Hopefully the collected annotations will lead to the development of better duplicate question detection systems, especially for StackExchange.
I've closed the other question as duplicate. With the only answer being link-only, I see no reason to merge it. Due to the dupe-closure, the two posts are linked together anyway, so it can be looked up easily. So in cases like this, you can vote-to-close if your reputation allows, or flag it otherwise.
Thanks for reporting!
It's a pity that StackExchange isn't a bit more intelligent with cross-SE site links. I'd say that the questions are related, but there's likely to be a slightly different focus by answerers on each site. I'd have thought an entry in the "Linked Questions" section would be the right way to do it, but not currently possible.
Placing a comment on the question that is going to cause a dup cycle is the right thing to do. Hopefully users working on the review queue will notice the comment and choose the right action (e.g. Leave Open). I also just noticed that the system prevents duplicate cycles (not sure if only direct cycles or also deeper ones).
If the cycle has already been ...
This is quite possibly my fault (though the system should probably handle it better). At the end of last week How do you link to applications in the Android market? came up in my Close Votes queue as a dupe of How to post a link to an android market app? but after looking at the two questions, it was obvious that one had old, out-of-date and (now-)incorrect ...
What is a duplicate answer?
A duplicate answer is an answer that does not add any information not alerady in an older answer.
What should I do about that?
Be sure to be on the duplicate answer, not the original one.
Leave a comment kindly saying that the answer doesn't add anything new to the question, and thus should be appropriately edited or deleted.
In general it's fine to have overlapping questions, as long as they weren't cross-posted by the same user (without appropriate reason). Linking in a comment is a good idea though.
This isn't generally done on beta sites though (the beta question is closed), although you'd have to ask the SE team for the reasoning there.