It's because of two years warranty, higher taxes, toll, and for more expensive items, smaller number of sold items.
It's not fair you singled-out Apple, since this is true for several gadgets I bought, software, or for example more expensive Canon lenses. It's not Apple specific thing.
My friend from the UK comes to the US to buy sports cars. His wife comes with him to buy clothes. While here, they also pick up iPhones. Not see what makes this a particularly Apple issue.
It's not fair you singled-out Apple, since this is true for several gadgets I bought, software, or for example more expensive Canon lenses. It's not Apple specific thing.