A fiscal responsibility to who?

Oh, that's easy: valve takes a cut on their platform. So Ubisoft can sell it lower on their platform because they do not have to pay valve.

From the filing:

Of those sales, approximately 75% flow through the online storefront of a single company, Valve. Valve’s online game store, the “Steam Store,” dominates the distribution of PC games. And Valve uses that dominance to take an extraordinarily high cut from nearly every sale that passes through its store—30%. This 30% commission yields Valve over $6 billion dollars in annual revenue. For everyone else, it yields higher prices and less innovation. 3. Valve is able to extract such high fees because it actively suppresses competition to protect its market dominance. Many other game stores have tried to charge lower fees, in the range of 10-15%, but they have all failed to achieve significant market share. This is because Valve abuses its market power to ensure game publishers have no choice but to sell most of their games through the Steam Store, where they are subject to Valve’s 30% toll. Steam Key Price Parity Provision. Valve nominally allows game publishers to make some limited third-party sales of Steam-enabled games through its “Steam Keys” program. Steam Keys are alphanumeric codes that can be submitted to the Steam Gaming Platform by gamers to access a digital copy of the purchased game within the Steam Gaming Platform, even when the game is not purchased through the Steam Store. Steam Keys can be sold by rival distributors including the Humble Store, Amazon, GameStop, and Green Man Gaming.
11. But Valve has rigged the Steam Keys program so that it serves as a tool to maintain Valve’s dominance. Among other things, Valve imposes a price parity rule (the “Steam Key Price Parity Provision”) on anyone wanting to sell Steam Keys through an alternative distributor. Put explicitly by Valve, “We want to avoid a situation where customers get a worse offer on the Steam store.”3 But that is equivalent to preventing gamers from obtaining a better offer from a competing distributor. The effect of this rule is to stifle price competition. 12. Because of this rule, Valve can stop competing game stores from offering consumers a lower price on Steam-enabled games in order to shift volume from the Steam Store to their storefronts. Even if a rival game store were to charge game publishers a lower commission than Valve’s high 30% fee, the distributor would not gain more sales because the game publishers could not charge a lower price in its store. Game publishers and consumers suffer because this rule keeps Valve’s high 30% commission from being subject to competitive pressure. The bolded section in particular makes it sound like Valve is forcing developers to pay 30% commission on Steam Keys sold on rivals shops when in fact it supposedly alleges (when you read the whole thing) that Valve is using its Price Parity Rule (which makes it so steam keys have to be the same price as their equivalent steam e-shop price) coupled with its popularity to force other shops that sell non-steam keys at lesser commission rates to fall inline, or alternatively that the game devs must offer their games for the same price as on Steam's e-shop even when using Keys provided by another supplier.

It doesn't explain (and I'm fairly sure that's on purpose) that this means that those same devs would charge the same amount on each shop regardless of who supplies the digital keys, and make more money on those other sites which benefits themselves.

13. This Price Parity Provision is one of the reasons why Valve has been able to continue to charge an inflated 30% commission for many years, even as that commission is plainly above the levels that would prevail in a competitive market. Competition would normally force such an inflated commission to come down to competitive levels—but Valve’s restraints prevent those competitive forces from operating as they would in a free market.

14. Because of Valve’s restraint, publishers cannot utilize alternative distributors to avoid the 30% tax that Valve has set for the market. Thus, they reluctantly market their games primarily through the dominant Steam Store where Valve takes its 30% fee. While several distributors have tried to compete with Valve by charging lower commissions on Steam Keys, those efforts have largely failed to make a dent in the Steam Store’s market share because publishers using those distributors had to charge the same inflated prices they set on the Steam Store.

Price Veto Provision. Valve also requires game publishers to agree to give Valve veto power over their pricing in the Steam Store and across the market generally (the “Price Veto Provision”). Valve selectively enforces this provision to review pricing by game publishers on PC Desktop Games that have nothing to do with the Steam Gaming Platform at all. Through this conduct, prices set in the Steam Store serve as a benchmark that leads to inflated prices for virtually all PC Desktop Games.

17. As explained by the founder and CEO of Epic Games (“Epic”), one company that has tried to compete against Valve, “Steam has veto power over prices, so if a multi-store developer wishes to sell their game for a lower price on the Epic Games store than Steam, then: 1.) Valve can simply say ‘no.’”4 Valve makes every game publisher accessing the Steam Gaming Platform agree to this Price Veto Provision.

18. Valve uses this provision to further enforce price parity and prevent rival game distributors from gaining volume by competing on price.5 And by inhibiting rival distributors from competing on price—even when selling games that have nothing to do with the Steam Gaming Platform—Valve inhibits potential competition against the Steam Gaming Platform as well, because rival gaming platforms cannot encourage usage by connecting to lower-priced distributors. Valve therefore protects its monopoly position in both of the relevant markets—the markets for PC Desktop Game Distribution and PC Desktop Gaming Platforms—through this provision.

It doesn't explicitly say that Valve make a commission on Steam Keys but lots of people seem to be of the belief that they do based on statements by Wolfire including in the filing. I would argue that they heavily imply this by leaving that context out of the filing entirely which is why half the comments in this thread have wrong information about it.

Specifically because part of the filing states that Steam is charging excessive commissions, which is something that is also stated in the Bloomberg article.

The fact that Steam Keys don't have a commission is integral to the reason why a developer might want to distribute them for a lower price on other retail sites.

However, I believe you are correct that this is not something specifically worded into the legal filing. The wording might lead people to believe this without specifically saying it.