When I first came across this in Free I immediately thought, that's not right:
And, by 2002, the Linux market share of the Web server operating system market stood at about 25%, compared to Microsoft's 50 percent.
I've pretty much followed these numbers on Netcraft for years. Here's their historical chart on this market going back to November of 1995. As you can see the Web server market has been a space long dominated by the open-source Apache HTTP Server:
Microsoft's market share appeared to peak at 38% in 2007, and has been in steep decline over the last two years.
If one looks at the numbers in the Fortune 500 space you still don't see numbers approaching 50%. This July of 2000 study reported on Server Watch shows Microsoft's share at 41%.
So what's the point of all this? Got me. I just don't like to see errors propagated. Maybe there's an explanation. I'd love to know where Chris Anderson got his number. A minor point I know, in what is a very well researched and excellent book in all regards.