The UNTOLD SUCCESS of Microsoft: Yes, it's Windows 7 • The Register

Looking likely Windows 8.1 == Windows ~7.5 (see, e.g., Microsoft testing Windows 8.1 update that hides tile interface by default [The Verge])

"Back-of-napkin estimates suggest that the actual number of Windows 8 devices in use is about 40 per cent lower than the number of licenses Microsoft claims to have sold.

Reller made no comparison to Windows 7 sales in her Thursday comments, either, and with good reason. Microsoft managed to sell 240 million licenses for that OS in its first year – 20 per cent more than the number of Windows 8 licenses that have shipped at the 16-month mark."

The UNTOLD SUCCESS of Microsoft: Yes, it's Windows 7 • The Register