Thats a different example. There is nothing immoral about living somewhere and buying somewhere else. Look at the people in SC who work in Charlotte. What is wrong is charging one retailer a tax without charging another retailer the same tax. Then you have the government acting as an agent against a retailer.
As for the business plan, Amazon is great, minimizing overhead and inventory. Nothing wrong with that.
In this case we have one retailer across the border in a no tax state and one retailer local.
We've already determined that it is fine for me to drive across the border to buy from them. Why wouldn't it also be ok to call them on the phone, or use the net, to order from them and have it shipped? It's the same exact thing. If they have no presence in the state then the state cannot force them to do anything.
Now the Texas case specifically is different because Amazon "may" have a presence in Texas. It claims that the distribution center is a legallydistinct organization. If it is, That is if Amazon pays the distribution center to send orders out, then Amazon has no presence in the state.
I'd guess it to be analogous to the Coca-Cola distribution method. Coca-Cola is based somewhere (Atlanta?) yet they have independant bottling companies scattered across the land. They don't own the bottlers, they just use them.