When Y Combinator gives $10,000 for a 7% stake in the company, the company goes from being "worth" $130,000 before the money to being worth $140,000 after, and they have $10,000 more in their bank account. Every dollar the company earns afterwards also increases their bank account by $1.00.
When an app store takes a 30% commission on sales, every dollar the company earns afterwards increases their bank account by $0.70.
The percent doesn't really matter (if YC took 30% ownership or app stores took 7% commission), the comparison doesn't really make sense either way.
