This is a really good power play - the idea being that if you can get more eyes than Steam can through your own store, go ahead, keep the money. But if you're

This is a really good power play - the idea being that if you can get more eyes than Steam can through your own store, go ahead, keep the money. But if you're getting the sale because of Steam itself, then we get the cut. You can still debate whether 30% is fair even if Steam are providing the discoverability but still, it's a solid policy and they're putting their money where their mouth is.