Top of this list used to be particular versions of Ubuntu
Summary: GNU/Linux "market share" in Steam grew by a quarter this past year, boosted by SteamOS perhaps, but watch the trends in distributions; even the Ubuntu-based distros aren't near the top (and SteamOS moved from Debian to Arch, so expect Ubuntu to stagnate further)
Saying GNU/Linux user-agents are just "bots" (Microsoft Lunduke and other Microsofters say this) is like asserting that the Twin Towers fell not because of two giant planes but because of explosives