I think they are referring to shipment share so this will be reflected in a few years in usage share. The world will be a better place if M$ does not get a bye in the market and has to compete on price and performance.
“Windows has 75% PC market share and the business productivity market where Office has 95% share by our estimates”
Forbes bases its stock-price estimates on a steady rise in notebook production. I expect notebooks will take a hit with the rise of smart-thingies which have huge growth. They do see a potential 10% drop in share price if M$ fails to capture significant share of mobile devices. That capture is not going to happen this year, so I see M$ falling in share of OS rapidly. According to the graphical calculator, if M$ slides to 50% share this year and 30% in the next few years, share price could drop 20%. Too bad, eh? Forbes calls it a “danger”.