This is not a proof at all. There is still a difference and that difference might be the key. Also, if you take all SO sites together, you still have the very

This is not a proof at all. There is still a difference and that difference might be the key. Also, if you take all SO sites together, you still have the very wide common topic "technical". If the topic becomes even wider, some clever tag-filtering/handling may be needed so a user could view the questions like they have been before. Also the reputation could be tagged base. In any case, just because not-so-well-made and not so technical-centered sites with not anywhere near the features of SO have failed is not a proof that a general answer site is a bad idea.