There is no requirement to use the App Store on a Mac.
And yet those programs do not magically work on Windows or Linux because that's not how computers work. Developers have to specifically target and build their programs for the devices they wish to support.
And many apps (in particular SaaS ones) allow you to buy one license and use their program on whatever device they support. App Store doesn't stop you.
No, but I'm sure you're aware that publishers/developers can make versions that run on each platform and license them in more consumer-friendly ways. I've bought non-SaaS desktop apps that come with license codes for each platform. If not included, there's often a discount for buying licenses for multiple platforms. And this doesn't require me to create an account for phone-home license validation. That type of license bundling is not so easy* and definitely less common with walled gardens.
* - I am taking developers at their word on this. I haven't sold anything on the Mac App Store.
That's an extremely rose/favorable look towards Apple which is doing everything in it's power to put itself into the relationship between a developer and a customer (to charge 30% and limit, limit, lock, block). Thats very evil.
And yet those programs do not magically work on Windows or Linux because that's not how computers work. Developers have to specifically target and build their programs for the devices they wish to support.
And many apps (in particular SaaS ones) allow you to buy one license and use their program on whatever device they support. App Store doesn't stop you.