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72% of devs believe Steam has a monopoly on PC games, according to study
(www.gamesindustry.biz)
Steam is a video game digital distribution service by Valve.
Steam News | Steam Beta Client news
Useful tools:
SteamDB
SteamCharts
Issue tracker for Linux version of Steam
I'm pretty sure that that only applies to steam keys being sold on other sites. If it's being distributed in some other form, it can be cheaper.