So, the figures are strongly biased. Let's look at the figures as they've been presented, along with a few simple calculations based on them. In all cases, SPA figures are in blue and my calculations are in red. Clearly, their own final figures contradict that statement. It's worthwhile commenting on how other analyses compare.
All numbers are in Millions of dollars and cover North American sales, only.
But they overestimated Windows sales by an even larger amount, so they still underestimated Mac market share. All numbers are in Millions of dollars and cover North American sales, only. Since the release of Windows 95 and the resultant media frenzy, they also underestimate Mac sales. By the time the final figures are released, they are old news and are never publicized. So the growing Mac market is constantly reported as dead while the modest Windows growth is exaggerated.