Stack Overflow is about creating a wiki of knowledge for future visitors. If you have a question that is only relevant to your specific implementation, and that will never help anyone else in the future, then it doesn't add value to Stack Overflow.
It's sometimes hard to know in advance whether your situation is unique or going to be of use to someone in the future however.
If it is completely unique and is of no use to anyone else, then it still of use to one person and still worth answering. Maybe SO just needs a flag for questions as 'unique situation' so it doesn't appear by default in future searches.
Also, SO isn't really a wiki. It's not designed that way. It's built around "this is my problem; what is the best solution?" interactions.
