My bet is that the user research would say the cast majority of iPhone usage is indeed personal, but that a major amount if iPad usage is shared, especially among children (and even moreso in poorer areas where an iPad-per-child isn't affordable). And I'd bet Apple knows this, but wants to maintain the fiction to encourage more sales.

It's like Amazon waiting forever to include Chromecast functionality to sell more Fire Sticks. I understand, but it's still degrading the user experience, and that just grates my cheese.