Well it's up to whoever runs the root DNS for the domain I guess. But I've never heard of a domain with a default. edit: oh never mind i'm being thick :)
And this isn't necessarily about people wanting to find apple's main website. Apple would have control over all subdomains and hosts in the namespace. They could give a subdomain to every app in the app store. So if you want the Pandora app, you don't navigate to Pandora.com were you might see ads for other mobile devices. https://www.pandora.com/everywhere/mobile You would go to Pandora.apple and only see the iOS mobile app.
And this isn't necessarily about people wanting to find apple's main website. Apple would have control over all subdomains and hosts in the namespace. They could give a subdomain to every app in the app store. So if you want the Pandora app, you don't navigate to Pandora.com were you might see ads for other mobile devices. https://www.pandora.com/everywhere/mobile You would go to Pandora.apple and only see the iOS mobile app.