I'm not a game developer and I don't know the Steam setup very well. I would genuinely love to hear from some 'serious indie game developers' though. Do they really think 30% is fair? Or maybe are they, like me, just accepting it and have no other real alternative (Hobson's Choice)...

Which is not exactly happily handing over 30% of your earnings to Steam/Apple.

Also, as mentioned in other replies, Apple explicitly blocks any other licencing path unless you're one of the big boys and can afford lawyers etc...