Blizzard is among those companies who still try to preserve the widest possible audience.
For example, the Valve is among them. But many competitors do not consider Windows XP as the operating system, disappeared from the radar even Windows 7, and in some cases 8.1. Compared to these companies, Blizzard is clearly kept to the last.
What it means one day of 2017 for your game from Blizzard or client Battle.net you will get a update that does not run on XP and Vista.
Judging by the forums, some users do still use outdated operating systems due to limitations of the personal computer, but other players are willing to sacrifice to support old OS for the sake of improving security.
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