Apple is WAY stricter about their store than google is. Google so so lax because they know giant devs would leave. Apple has gotten away with being a gate keeper making these apps play nice because there was no alternative.

Small companies will not move unless a third store really takes off. It is the big apps that everyone wants that will have the market power to move. Like Facebook, Instagram, Google Chrome, Microsoft, possibly Adobe, and all the streaming apps like Netflix.