That is a consumer study - it ignores the vast number of system that are used in businesses.
And Apple does not pursue the enterprise markets... although their share in that market has grown as well. That is why the US Apple market share, while 21% among consumers, is only 10% when all computer sales are considered... but it is climbing rapidly. Third quarter of 2008, Apple sales increased 22% year-over-year compared to only 3.5% year-over-year for the entire computer market in the US. it was even more than that for the rest of the year—around 30% while the rest of the PC market was declining by 1%.
In addition, study after study, show that Macs in business have a greater Return on Investment, a Lower Overall Cost of Ownership, and far lower requirements for IT intervention.