Retaliating against employees for discussing their working conditions is in fact enormously legally risky for a company. Doubly-so when doing it via SLAPP lawsuits. Why on earth would Valve take the risk?
yes, exactly. Esp. if he is the only one talking about it this way publicly. If it's truly awful, employees will vote with their wallets and quit.
And if valve wins the law suit, what reward would they have gained, other than stopping him from saying what he has already said (which cannot be taken back). There might be punitive damages to be paid, but it's not like the corporation is going to make money from doing so.
And in fact, making a law suit would legitimize the claims!