Hello there :-)
It's a good oportunity to put some clarification:
Steemit is not taking any part of your rewards.
Votes make post to earn certain amount, but until payout time it's just potential reward.
After 7 days:
- 75% goes to the author rewards (can be shared with beneficiaries)
- 25% goes to curator rewards (can be less - those voted very early, as anti-bot measure are returned to the pool), those are very important because it incentivize people to vote for your content.
Some applications can set beneficiary reward in a way that they take some % of author rewards. It's up to them to set it accordingly. Setting it to zero makes them figure out some other way to earn funds to stay alive. Setting it to high ... as we can see here - can discourage people from using the app.
I'm not sure if 10% is high or not. Depends on the app I guess.
From my personal point of view, something between 3-5% could work well, but I would consider 5% as a high end, that only apps with exceptional UI/UX can survive setting.