If you bought an iPhone last quarter, your Apple Tax was $252.
You can't see it in terms of cost-plus, you have to see prices in terms of marginal utility and premium over supplemental good. If an iPhone and a Galaxy S6 do the same thing, and the ASP of the Galaxy is $6 less, that's the baseline.
So then you can either say, either the Apple Tax is $6, or the Samsung discount is $6. And then you have to ask why exactly is Samsung selling phones short when they (putatively) have the same value? And why does Samsung even bother selling phones at the bottom of the range if they lose money on every sale? And if Apple is able to turn their profit over costs into marketing that buys them significant pricing advantage, why can't Samsung do the same thing?