What is different between those Stack Exchange sites?
What is meta?
- Any Stack Exchange user can ask a question
- The community provides support, votes on ideas, and reports bugs
- Your voice helps shape the way Stack Exchange operates
The difference is reported in their FAQ pages.
In the first case, a question about the http.conf file for a website you control is on-topic on that site, but it would not be on-topic on Stack Overflow. In fact, Apache http.conf allow intranet was migrated there from Stack Overflow.
In the second case, a question about programming in Facebook would not be on-topic there, as questions there are about using Facebook, not creating a Facebook application, which would be on-topic on Stack Overflow.
Simplifying, the topics are: