I'd argue appliances should be walled and computers shouldn't be.

I think the form factor is very relevant. A MacBook is treated like a computer. A phone is treated like an appliance.

Most phone/tablet users want the convenience of modular functionality without vetting the source. Said functionality should also be easy to discover and add/remove, hence app stores.

Whereas on a computer, app stores are ignored if they even exist. Most people install after doing their own Googling or seeing it run on another MacBook.

In my opinion phones intended for general purpose computing should have distinct marketing and different software-related features.