Arguably they said the same thing about the "stylus". iOS devices will always be touch-first, but there's no reason Apple couldn't add an accessory as a secondary input mechanism (though as you say, perhaps not for navigation). I mean, if you can have Made for iOS game controllers...
There is a reason, but you won't like it. Apple works in a certain way - depending on your view, they either don't compromise unless they really have to - or act like they don't compromise in a well thought-out performance.
Either way, they would never add a mouse to a touch device because
1. Unlike Microsoft, they believe touch is an alternative, not a supplement to mouse input
2. Adding mice would send a message that touch is flawed for UI interaction (Pencil is different, but let's not go there now)
3. It would create confusion among some users: "Do I to use a mouse or touch?!". There is no confusion for the Pencil because it's historically embedded into our work patterns - everyone knows when to use them. People want to be told how to use something and focus on the results of the tool, not the tool itself. This is Apple's customer's viewpoint (it's also the reason Android and Windows fans like to call Apple users "sheep", which just shows how they miss the point)
4. Allowing the mouse would enable deveopers to rely on them. This means they would make apps designed to be used with a mouse. Then, suddenly, not only would you prefer a mouse for some apps, you would also - by logic - have to prefer working on a desk instead on the couch. In other words you'd get a "Mac" running iOS. Next thing you know, people would want to replace that iOS (whose only real benefit over OS X on tablets is that is designed for touch). So, basically, you'd get a full Mac with a touch screen, which is what many people here would want but Apple will never do.
