Google/Apple where is the catch?

Browsers look more and more capable as an application deployment platform. They give developers a chance to bypass those pesky issues of being at a mercy of Apple/Google/Whatever app stores.

For example since browser currently exposes Bluetooth LE and WebGL I am thinking of moving one of my products (namely virtual bike training platform) to a browser.

If I do this, then how Google/Apple will control me then? Or they will at some point require web apps to be certified (practically turning it to another app store) to run on their browsers?