Not saying your wrong as I don't know but does steam really get 70%. Why would anyone use them then?
Yeah, it's about 70% last I heard. If you sell a game to 2 million people and get 10 bucks each that's a ton of money. If you try to sell on your own you will get more money per person but you will probably get 1/10th the sales.
There's also the benefit they get out of early access, in that they get the game to the person.
To my thinking the big benefit of steam is to sell your game there AFTER you have made your initial sales and got as much as you are going to get on your own. Not only do you get money off steam but remember you get a lot of exposure. So if you release your game on steam then you run a kickstarter the next year you probably will get way more pledges, assuming they liked your first game.
I see how it looks like they are getting some huge gain off the beta but they probably just set the price high to encourage people to NOT get the game this way. Personally I think a very small alpha/beta is a lot more useful to a coder than a great big one with millions of duplicate bug reports rolling in, probably they feel the same. But by going on steam for early release it gives them an easyw ay to push out access to ALL beta testers not just the ones who buy in now.
So steam kinda sucks, but it has its good side as well.
When I someday release my game, it will eventually go to steam but I would never use that as my starting option or else your game will be priced at 5 bucks and you will get only 30% of that, and you have to hope you sell a million copies or you can forget about doing a second game.