Can you sell it on myWidgetAppStore? Can someone install myWidgetAppStore that sells apps? (the way I can visit myWidget.com if I don't want to use Walmart.com, because Safari doesn't block other websites but iOS blocks other appstores)

On Apple app store you can't sell on other stores to the same customers. If you extend your abstraction to say that Android and Apple are two neighborhoods, it's like to say that Apple app store have a monopoly to sell in Apple neighborhood and for you to sell to people that lives in Apple neighborhood you have to pay apple 30% and use their payment system.

But on Android neighbourhood you can sell in other stores, or even create your own store, if you don't like to use android's app store or pay them 30% or use their payment system.

Some people living in Apple neighborhood says that they prefere the Apple app store monopoly because they can be sure that Apple store is safe to shop and there is only good products.

Because you are not forced to sell exclusively at walmart. You can sell your product at any store and people can get to it. Because of the walled-garden nature of the iPhone and iPad, the only way for people to get apps and make purchases for those apps is via the App Store. So, in your comparison, you would only be able to sell at walmart.