Yes, materials can make a product look and feel premium. But in many cases they can in fact make it less durable - case in point, glass iPhone 4.
Apple tax is just another name for profit. If Google can sell a 32GB Nexus 7 for $249 there is certainly more than enough room in pricing. Lets not forget that Apple gets lower prices for sourcing components since they place such huge orders.
Google will have also placed massive Nexus orders, likely for 10 Million + units. Are really going to argue it makes much difference after 10 million units?
Again you are ignoring the more expensive materials and the larger screen and other parts. It will cost more to build an 8" Aluminum Mini, than to build an 7" plastic nexus.
They have the highest profit margins of any consumer electronics manufacturer. There's nothing wrong with that, but that is the definition of overpriced.
No it is being smart, by not following it's competitors in a race to the bottom, that would suck out all the profit margins.
If I am selling my product for 30% profit margin and my competitor is selling it for 0%. I am not overpriced. I am fairly priced. My competitor OTOH is an idiot, who would soon be out of business if his only income is selling such products.