Vidalia only grow in that one spot because Vidalia onions are regular sweet onions grown in a sulfur poor environment. The sandy soil of Vidalia, Georgia causes sulfur to run down through the soil into the water table instead of settling near the surface to be used by plant life. This results in low VOSC content in the onions reducing the burn from them. The most notable of these VOSCs is Allicin ,a compound which when exposed to oxygen, acts basically like tear gas to us humans.

Edit: de-shatnerized

The growth thing is true as well, wasabi is very particular about the soil and water. Iirc, most of it is grown on one farm in Japan fed by a stream that runs through and irrigates the soil.

It's worth noting that if you're not on a windows machine or a OS X machine you may need to manually configure TRIM, as many *nix distributions do not have it enabled by default