This offer differs from historical offers preceding the launch of new versions of Windows as it is being made available for free to existing users in addition to new customers after the offer announcement We evaluated the nature and accounting treatment of the Windows 10 offer and determined that it represents a marketing and promotional activity, in part because the offer is being made available for free to existing users

If it said Windows 10 was an upgrade, not part of a marketing campaign, the company would have had to adjust Windows revenue to account for the deferrals -- and set aside money from sales of the OS starting in January when it announced the no-cost upgrade -- reducing Windows' earnings for at least the first half of this year, perhaps longer. That could have painted an even darker picture of Windows revenue, maybe one that would have bothered skittish short-term investors enough to impact the stock.