App developers are unlikely to take themselves off the Apple store it would remove themselves from a huge portion of the market they developed an iOS app for.

But they will find third party stores taking a smaller cut than Apple does. They will pass on some of that saving to the customer or find a way to encourage you not to use the Apple store if they get to keep a higher cut. Like earlier updates and feature releases.

That's the point. Apple currently has a controlling monopoly on a market. Competition will lower prices for the consumer.

Anti-trust laws exist to do exactly this.

All it will take is a trustworthy company to launch a 3rd party app store. Then maybe you won't mind.

Some companies like Cisco might just launch a store instead of putting their apps through Apple as they would like higher security than the App store provides.

Apple will also be forced into a competition to be the most secure app store too.

The likelihood is they'll just play with the margins and do what's necessary to keep a near monopoly but the possibility of competition is useful in itself. At the moment there isn't even that.