Terroir is a key concept in viticulture because it relates to the bodily characteristics of wine in respect to the environmental and socio- economic conditions in which the grapes are grown.
Grading the quality of wine and wine style most likely, to a large extent, can be explained by terroir. (The winemaker and his process may quibble at that)
But, terroir is very difficult to study on a scientific level because many factors are involved, including climate, soil, cultivation and human practices, all of these factors interact.
The best expression of terroir is achieved when the capacity of the grapevine variety is suited to the local climatic conditions in such a way that full ripeness of the grape is reached by the end of the growing season; Not every grape can be grown in very place.
Also, grapes are an extremely climate sensitive crop and vines have been cultivated for several thousand years. What has happened is that over time many grape growing regions have been recognized, whose specific climatic conditions matched the capacity of certain varieties to produce wines of distinctive character.
To produce high-quality red wines, environmental conditions should encourage reasonable vine strength, either through practical water shortage stress or through low nitrogen supply which comes from surroundings with shallow or stony soils, in temperately dry climates. Likewise, regular but not excessive vine water and nitrogen supplies are needed to produce high-quality white wines.
However, great terroir emerges almost only when socio-economic conditions are satisfactory to the establishment of quality-orientated wine production. These conditions are is often measured as a combination of education, income and occupation. As we know, examinations of socioeconomic status often expose inequities in access to resources, plus issues related to privilege, power and control.
Those with more money and better access have more opportunities...and you have chances at better Terroir because of it. It's just the way it is.