It's not "high", it's extremely high. They just have a few hundred employees while making several millions of profit per employee. More than Apple. They are printing money.
> valve is certainly not rent-seeking. it offers service that is valuable to users,
A 30% fee just for hosting the game is not valuable.
> and take care of online infrastructure for games published through it, indefinitely, at no running cost to the developer.
The cost is substantial. It costs the developer 30%. That's a huge chunk of the total revenue. Hosting a game is very cheap, and could probably be done with less than a 3% fee. Often Valve will make more profit from a game than the developer itself. Sometimes the developer will lose money (after subtracting development cost) but Valve will still make a big profit with that game.
Their high profit is indicative of the high level of value they provide. They're far from the only store to buy/sell games in. Steam's users use Steam because they prefer it to the alternatives.
While I can't argue whether 30% is actually fair, I do believe you are disregarding some benefits steam brings which may seem trivial. The hosting of online-games and facilitation of sales is not their only service. One that has traceable value that immediately comes to mind is the illusion of a central authority for achievements.
I have personally purchased many titles a second time to register my feats with steam and anecdotally see similar sentiment among older gamers. Achievements feel worthless in isolation but provide fulfillment when socially recognized. These are sales being manifested solely through Steam's position.
Now, back to whether this social permanence is worth the 30% Steam is extracting, I do have my opinions. Steam is technically "rent-seeking" from a strict economic classification, but is this more-so a case of the lighthouse or the railroad?
its probably low compare what customers and game developers are willing to pay for it.
hosting a game and running a store nowdays is very easy, but still games launch on steam rather than building their own store or using a steam competitor. if the cost was too high, people would not be using the service
> valve is certainly not rent-seeking. it offers service that is valuable to users,
A 30% fee just for hosting the game is not valuable.
> and take care of online infrastructure for games published through it, indefinitely, at no running cost to the developer.
The cost is substantial. It costs the developer 30%. That's a huge chunk of the total revenue. Hosting a game is very cheap, and could probably be done with less than a 3% fee. Often Valve will make more profit from a game than the developer itself. Sometimes the developer will lose money (after subtracting development cost) but Valve will still make a big profit with that game.