We've been educated (or bullied, depending on your outlook) by foodies like Alice Waters and Dan Barber to adopt the European concept of terroir—the best stuff to consume is the stuff grown in closest proximity.

Terroir has absolutely nothing to do with proximity. It is the idea that the place imbues the product (wine, apples etc...) with qualities unique to the region. In other words, the same grape varietal grown in a south facing vineyard might have different qualities than the vines grown on the north side of the same mountain.

The concept you were probably looking for is the 100 mile concept, where you'd want to consume foods grown within a hundred miles of yourself in order to maximize freshness, eat foods in season and reduce environmental impact from shipping stuff around the world.

Exactly. The idea of terroir actually enrourages people to buy from places far away, even if similar products are made locally. The idea is that people should produce what suits there region, rules be damned. That's why so many French wines are amalgamates of different grapes - so they can capture whatever the vineyard believes its "terroir" should express. It's almost an artistic license. It has absolutely nothing to do with what you consume.