Google isn't offering exclusive native access to a platform and isn't hosting content... they're simply offering payment processing and a storefront. 5% is nice, but can't be compared legitimately with Apple's 30% cut.
So, I would say the title is misleading. 5% does seem like a fair cut for handling payment processing and storefront, but it's not like Apple is charging anything for access to a web app. They're just not providing a storefront to do it with.