I'll happily pay these 30% if it means I get quality services for them:
- high speed download servers
- reliable cloud saves
- automatic, non intrusive updates
- discussion forums
- easy mod management
- friend networking, multiplayer services
- responsive and uncomplicated support
(using Steam as an example here)
People always act like those are to be taken as granted, but if you have ever worked in dev/devops, you would know that there's a lot of work maintaining each one of them.
Also, you can use these services for as long as you want, despite paying for them with a single one-time purchase.
Of course, if the platform doesn't provide any services or benefits, your point stands. In that case just avoid it.
My two cockatiels Oreo and Kiri preening each other