Well, the polls always have the last word! Irrespective of the small sample we have had, I would consider the responses as a microcosm of reality- and yes, leadership is the most important determinant of culture in the organisation. Research tells that leadership has a 2x power of influencing culture- well, they are the guys who are running the show, aren't they! Moreover, the woman/man at the very top has an even greater influence. 
What then are the challenges in getting leadership to drive a distinct culture? First things first - we have to get alignment at the top on the culture we need. And quite often, this is not easy as this co-ownership has to be quite deep, and based on real alignment of values and intent. This journey of building alignment takes time, it has its ups and downs, moments of truth and catharsis, and sometimes confrontations. This then is the role of the leader of the top team- he has to believe in getting this deep alignment, and work through a series of experiences and interventions to get to a stage where the top team is in full sync. 
But this is easier said than done! There are the usual obstacles to such meeting of minds and hearts. First, the leader has to believe that it is critical to get this alignment, and should work consciously and patiently on it. Second, despite the best intentions of all great leaders, how many have the luxury of time to prioritise and focus on this area- the short-term business pressures on modern day CEOs are all-encompassing, and don't leave much room for them to focus on such issues, except for the most prescient and focused of the leaders. Third, longevity of the top team is critical in this journey- they need to spend enough time together as one group. Too much of people moving in and out of the top team saps the energy. And last, given that this is a task that requires a lot of reflection and work on an emotional plane, the leader needs to have a great counsel or coach to help him through this lonely process.
Being a visionary and charismatic leader probably makes things a bit easier- the way Steve Jobs or a Richard Branson can bring their personality to bear in pulling together a culture that they passionately believe in is something not all can do. However, there is the obvious danger in being too much individual leader driven while we build the culture of an organisation. 
As Rosabeth Moss Kanter says, 'in the middle, every change is a failure'. So would it be when we build an aligned culture agenda with the top team!