I've been trained as a Black Belt, and recently received my "Certified Quality Engineer" certification, and it struck me while studying for the CQE exam exactly why Six Sigma is so popular. First, a quick clarification on the differences: the CQE certification really goes "soup to nuts" in terms of all phases of quality management, while Six Sigma, at least as I was taught, really concentrates on the statistical methods.
So why, then, does the partial course get more billing in many places than the full course? My take is that many companies that practice Six Sigma--including one I used to work for--really, really, really don't want to be confronted with quality principles like those of Deming, and really, really, really, really don't want to be told, as Deming famously is said to have told Ford executives, that 85% of their quality problems lie in the executive offices and board of directors.
Or, it could be just that Six Sigma is the most recent fad, but I have to wonder if many executives are passing up on the benefits of more comprehensive quality management because too many important toes would be stepped on.