I am conflicted. I love Valve, but 30% seems like a lot. On the other hand, I doubt the developers are being charged for the bandwidth or for Steam platform integration. Which means that long after the developer has walked away with their money for the sale Steam is still providing licensing management, platform integration in the form of user management, and the bandwidth for every time the user redownloads the game at 0 cost to the user.

While that fee may seem high, the developers are in someways subsidizing other developers that could never afford to build and maintain that infrastructure. They're also reducing the friction and on-ramping of new players/users. They are also providing the payment processing and handling billing/chargeback resolution.

Just the merchant fees alone would be would be 2-4% of revenue (not including losses to chargebacks and fraud/risk controls). The raw cost of bandwidth usage would be ~2 cents per 12GB game download (not including infrastructure to host/facilitate the amount of simultaneous downloads). The staff to manage billing issues/refunds. The raw amounts are small, but not insignificant considering that for every $20 they collect on a AAA title there are several indie games getting all the same functionality which only nets Valve $2.

Valve, Epic, Playstation, Xbox. The platforms are providing the ecosystem and platform that has allowed gaming to flourish at incredible rates, outpacing the motion picture industry and the sport industry.