The difference is, Apple's 30% is a requirement to do business on their platform. Apple can charge whatever they want because there is no competition--you're not allowed to use other providers. Your only option is to leave iOS, which isn't really an option for a lot of companies.

Google isn't mandating anything; if a company finds 10% to be reasonable for the services provided, they can make use of it. Otherwise they can do it themselves, or use another provider.