"If that killer app vendor decides to support Android more effectively than they support Apple, or if for some reason they decided to drop the iPhone, that one vendor could have a devastating effect on Apple's position in the marketplace"
Right. But this could have happened at any point once Android became a legitimate competing platform, and that's where the argument loses steam for me.
Except that it could happen now. It's basically nonsense. Almost every popular (non-gaming) app that is not directly from Apple has a dual on Android, and the sky hasn't fallen for either platform yet.
"If that killer app vendor decides to support Android more effectively than they support Apple, or if for some reason they decided to drop the iPhone, that one vendor could have a devastating effect on Apple's position in the marketplace"