I'm less mad at Steam and Google because there are clear, simple ways to avoid their cuts.
I have no basis to say whether they're providing a service worth the 30% charge. I'm also less mad at Steam than at Google because they're being less shady about trying to push people into their store too.
Yeah, Steam is pretty much a monopoly. But I haven't seen what I'd call monopolistic practices from them. It's just that everyone else appears to fall flat on their faces when trying to make a competing product.