In a nutshell, the NTSB is responsible for ALL aircraft incidents. However, there are only handful of NTSB investigators. Because of that, they look to regional FAA offices to do investigations of the relatively minor events. If it ireaches the level of an accident, it will usually go on the NTSB database. Incidents don't always make it there. The ASIAS site posts minimum information about the accidents and incidents but does not provide the indepth analysis the NTSB accident reports do.