Interestingly, W7's losses to WX track pretty closely with another trend that Steam Survey watchers have been keeping an eye on in recent months: the rise (and now fall) of Simplified Chinese as Steam users' language of choice:
The last few months' surge in Steam market share of both W7 and Chinese had been attributed to the surging popularity of PlayerUnknown's Battlegrounds (PUBG) in China.
PUBG is still the top-selling game on Steam, a position that it's now held for nearly a year, and it's unlikely that we'd have heard anything about declining PUBG concurrency numbers, since attention tends to be paid only when concurrency records are being broken, but it's possible that PUBG's popularity has finally cooled the slightest little bit, allowing market norms to reassert among Steam's users. Keep an eye peeled in the coming weeks for stories about PUBG "dying," though, since the other thing that media outlets of all types love is a good "falling from grace"narrative.
Still, it looks like WX is finally starting to climb back towards parity with W7 among Steam users, even as Windows overall loses users to OS X, which is exactly what we see in the broader OS market, too. For a change. This is just one month's data, though, and you know what they say about once being a freak occurrence; I'll want to see three months' of consecutive WX gains in the Steam Software Survey before I'll call this a real trend.
There's no denying that these numbers fit with the overall trend, though. We'll just have to wait and see if the trend continues into next month, or if WX starts to eat into W7's overall market share more in coming months than it's done to date.