Sources for this:
https://storage.courtlistener.com/recap/gov.uscourts.wawd.337957/gov.uscourts.wawd.337957.1.0.pdf
99. Steam imposes the PMFN through more informal guidance as well. Steamworks Development is a forum where publishers interact with Valve employees. On this forum, when one publisher asked Valve about the “rules regarding distributing/selling a game outside of steam” in a thread called “Patreon and steam keys” dated July 2, 2017, “TomG” of Valve explained how the policing system works: “The biggest takeaway is, don’t disadvantage Steam customers. For instance, it wouldn’t be fair to sell your DLC [downloadable content] for $10 on Steam if you’re selling it for $5 or giving it as a reward for $5 donations. We would ask that Steam customers get that lower $5 price as well.”
101. The same “TomG” also explained to another game publisher that the publisher should “[t]hink critically about how your decisions might affect Steam customers, and Valve. If the offer you’re making fundamentally disadvantages someone who bought your game on Steam, it’s probably not a great thing for us or our customers (even if you don’t find a specific rule describing precisely that scenario).” In that same thread, TomG responded to a question by stating: “we usually choose not to sell games if they’re being sold on our store at a price notably higher than other stores. That is, we’d want to get that lower base price as well, or not sell the game at all.”
102. Additional examples of Valve’s PMFN enforcement abound. On December 3, 2018, for example, a Steam account manager, Tom Giardino, reportedly told publisher Wolfire that Steam would delist any games available for sale at a lower price elsewhere, whether or not using Steam keys. A Valve employee told another developer that if he “brought a particular other game of [his] to Steam, it would need to be equivalently priced. This was regardless of whether the non-[S]team version use Steam technology[,] [i.e.], a completely standalone version would have to be the same price as the Steam version.
Valve's response here: https://storage.courtlistener.com/recap/gov.uscourts.wawd.298754/gov.uscourts.wawd.298754.309.0.pdf
https://storage.courtlistener.com/recap/gov.uscourts.wawd.298754/gov.uscourts.wawd.298754.127.0.pdf
200. In late 2018, for example, one publisher had been selling its game on the Steam Store for $5, but launched its game on the Discord Store (enabled for Discord’s gaming platform) for free. Valve detected that the publisher was charging different prices on the two storefronts, and told the publisher that offering its game for a lower price on Discord violated the Valve PMFN. Valve insisted the publisher renegotiate its deal with Discord and ensure that gamers buying the Discord version pay the same price as gamers buying the Steam version.
201. Valve’s enforcement of the Valve PMFN harmed Discord, publishers, and gamers. Discord was unable to use price to grow its share of the market. Publishers were unable to reap the benefit of Discord’s lower commissions. Gamers were denied the ability to purchase the game for a lower retail price.
202. Other publishers have received similar explanations from Valve. One publisher contacted Steam through the Developer Support tool, as instructed in the Steam Keys Rules for questions about how “to avoid a situation where customers get a worse offer on the Steam store” and remain compliant with Steam’s rules. The developer asked, “Regarding the pricing policy, can a non-Steam variant of a game be sold at a different price than on the Steam store page?” Steam’s response was “Selling the game off Steam at a lower price wouldn’t be considered giving Steam users a fair deal.”
205. In response to one inquiry from a game publisher, in another example, Valve explained: “We basically see any selling of the game on PC, Steam key or not, as a part of the same shared PC market- so even if you weren’t using Steam keys, we’d just choose to stop selling a game if it was always running discounts of 75% off on one store but 50% off on ours. . . .”
207. A Valve employee told another developer that if he “brought a particular other game of [his] to Steam, it would need to be equivalently priced. This was regardless of whether the non-[S]team version use Steam technology[,] [i.e.], a completely standalone version would have to be the same price as the Steam version.”
208. Wolfire has been subject to Valve’s threats to enforce its PMFN. On December 3, 2018, for example, a Steam account manager, Tom Giardino, told Wolfire’s owner that it would delist any games available for sale at a lower price elsewhere, whether or not using Steam keys. As a result of Valve’s enforcement of its PMFN, Wolfire has not offered its games for a lower price than what appears on Steam with other sellers. Had Wolfire been able to discount its consumer price with other sellers, as discussed below it would have sold more games at a lower price (and a higher profit) for Wolfire. Valve’s PMFN blocks Wolfire and other developers from selling their games at the output-maximizing and profit-maximizing price, as dictated by the economic forces of supply and demand.
Valve's response here: https://storage.courtlistener.com/recap/gov.uscourts.wawd.298754/gov.uscourts.wawd.298754.128.0.pdf