When I worked for a large developer that in turn worked for a large publisher, they took 100% of the first 1 million purchases, and 95% of every purchase after that.
$100 once is ok but not charging about 30-40% for every purchase.
Most of our games did not sell anywhere close to 1 million copies, so there were no royalties paid
However, they did pay for most of the development costs, so we at least always almost broke-even, even though there was no profit.
Giving only %30 of your income to the sales & distribution part of your business is an amazing deal.
If you were to try and sell your product in physical stores, you'd be losing at least 40% of your sale price to retail/distribution overheads.
If you set up your own online store, you might pay much less for distribution (assuming you get a good price from your hosting company -- keep in mind Steam lets me download terabytes of data at multiple MiB/s all around the world), however, you'd instead have to pay a fortune in advertising in order to get as many visitors to your site as people who visit the steam store.