This... misses the point? Of course the can not sell on Steam. That's always an option.

The antitrust aspect of all of this is that Steam is the de-facto marketplace, consumers are stubborn and habitual and aren't as likely purchase games less-known platforms, and that a publisher opting not to sell on Steam might have a negative influence on the games success.

If that consumer inertia gives Steam an undue advantage that wouldn't be present in a properly competitive market, then it there is an antitrust case to be made, full stop. At this point, the court will decide if the advantage is significant enough to warrant any action, so there's really no need for us to argue further.

But I really don't like seeing Wolfire—which is a great pro-consumer and pro-open-source studio—having their reputation tarnished just because Lemmyites have a knee-jerk reaction to bend over and take it from Valve just because Steam is a good platform.

Steam runs weekly deals and daily sales all the time. I doubt they have to check with gog.