Valve does have a commanding share of the PC gaming market.
But they don't have a monopoly if you account for the *entire* gaming market. (Mobile, Home Consoles, Handheld Consoles etc.)
With that... A monopoly by a company like Valve would be very different to that of say... Electronic Arts, Microsoft, Sony etc'.
Valve is a privately held company, it doesn't need to answer to shareholders and their ever-increasing demand for more profits.
--::{PC Gaming Master Race}::--