Apple's position related to zaps will surely be copied by Google in the months ahead. Surprise, surprise: Greedy companies are greedy. I expect Amethyst to go through something similar with the Google Play version. Even if Android does offer ways to sideload the app, most people "don't have time for this BS" and will continue to use these app stores.
And it's their free choice to do so.
Gotta pay the bill, though.