Your logic is quite flawed. Nordstrom does not have a duopoly on retail clothing. I'm pretty sure if Nordstrom controlled 60% and Kohls had the other 40% marketshare, and they attempted to exert unfair control things would be different.
Bottom line is smartphones are now considered a basic utility (like phone service, power, etc. ) all those industries are regulated since consumers wont have choices, for example if i'm unhappy with my electric provider, I don't have other options. Apple made a business decision to lockdown the $1k phones we bought and prevented customers from being able to download and install apps unless we go through their app store. With this in mind, they are charging app developers a highway tax to be able to install on our phones. They can also remove apps based on whatever they want. This is too much control. If we had alterative app stores on our phones, we may be able to buy apps cheaper on another store, vs. apple's app store. But we have no choice.
With apple controlling over 55% US smartphone and Google with the other, they are a Duopoly and are highly subjected to regulation.
The question I always ask is, why am I able to install apps on my Mac or Windows OS without being forced into the MS app store. There is no reason this can't work on iPhone. Apple has made a business decision to make it this way, and they are abusing it. This will not last forever.
The issue with comparing android/google to apple in terms of app stores and control is that.
1. Google allows other payment sources.
2. Google allows 3rd party app stores.
3. Google allows side loading.
4. Google allows 3rd party side loading.
5. Google allows you as a user to use Adb to install applications.
6. Apple prevents other payment sources.
7. Apple prevents 3rd party payment sources.
8. Apple Prevents side loading.
9. Apple Prevents 3rd party side loading.
10. Apple Only allows User installed applications through MDM and a dev license thats 100$ a year.
11. Google does not prevent develipers from linking to a website to bypass googles payment source.
12. Apple blocks any and all mentions to a website or any method of trying to sell services or digital goods through anything but apple. You can't even tell the user you have a website.
There isn't much of a Duopply in a sense. There is only 1 manufacture fully locking everything down.
Google makes the android operating system and you are able to take it with google updates to AoSP and use it for free.
There are some cases where you need to include the google store etc depending on licensing. But you are not FORCED to include google services when you can make a phone with AoSP.
On google phones you can unlock them to install your own operating system or remove app stores and install your own.
With apple you can not remove key system services and can not install your own App Stores.
The reality is... Something people "here" do not like to accept and its ****in truth. Apple is has been and is becoming more of a bully to try and force other companies to not offer services.
In todays modern age a phone is not always a luxury and in many cases its a necessity. You have one company "Apple" making it as expensive as possible to use the device and any 3rd party services, and you have google who well with free AoSP basically made it possible for manufactures and app devs to be able to reduce costs and make things affordable.