Indeed there are many free-to-play games on Steam with micro-transactions that are not required to give Valve a cut.

Just to be clear, in the DCS World example you do have to make a choice between using Steam for the game download and purchases, or to use the Eagle Dynamics website/downloader directly. External modules purchases do not import to the Steam account, IIRC.

My point was probably that Steam doesn't force users to only use their platform.

To further illustrate the non lock in culture, you can do a transfer of content from Steam into your Eagle Dynamics account if you want to change the account type.

I'm guessing that seasoned DCS players like the direct account method (more frequent sales, for one), whereas beginners are more likely to discover it through Steam.

(iRacing also has a similar relationship with Steam, although in that case Steam only managed the subscription - not the car/track purchases.)

They are required to for in game purchases, but they are likely too small for Valve to care else have a custom agreement with Valve.

I believe the rule you're talking about only applies to literal in-game transactions - i.e. the binary you put on steam cannot itself implement a non-steam wallet. But there's no business rule against selling in-game content elsewhere, like apple is doing.

I claimed Steam was similar. I did not claim that they share all of the same policies.

TFA is about Apple's policy on purchases that happen outside the app. It used to ban even linking to them; now it allows that but it wants a cut. Steam doesn't do anything similar - it has no rules about purchases outside the app.

Steam is not comparable because it is not a first-party platform.