I strongly recommend watching the NTSB news conference that someone has linked a few pages back. Apart from stating a few facts regarding the speed just prior to impact the chairman gives an insight into the exhaustive nature of the inquiry.
She also makes the point that nothing is ruled out and that human factors will be fully assessed eg training records, CRM, operations manuals etc.
The point is the NTSB have an open mind about the crash and collect whatever data they can/need to do the job. The "culture" of the airline, if it proves to be an issue, will, I am sure be revealed if it proves to be a factor.