You didn't really address any of what I said: the Linux ecosystem is hopelessly splintered in ways Windows will never be, so what Valve is doing amounts to bringing gaming to SteamOS, not Linux. Developing a game that supports XP and up is much easier than developing one that supports every flavor of Linux, and this is going to ruffle some feathers here, but Windows development is just easier in general. The tooling is far more mature than what the open source community has offered, and MS has furthered the divide year after year. There's a reason pretty much every AAA game is developed on Windows. Say what you will about proprietary software, but there are advantages to having someone else conduct ecosystem testing. Most game shops simply cannot afford to effectively and sustainably test their software on the multitude of Linux distros and hardware configurations out there.
If, at the end of the day, dual booting SteamOS is a requirement to reliably play games, I don't really see this as a solution to the Linux gaming problem. If I have to dual boot, I'll fork over the money for a valid Windows license so I have access to a much, much larger library of games, drivers that fully utilize my GPU, etc.