nothing to do with race. But more with wisdom and ability to see reality through experience. The middle class in so called developed countries are more the hard working professionals etc. They are trained disciplined and financially at a level where they have seen the superficial (material)good of the world as well as the realities of life as nothing has come easily. This has broadened their WISDOM to a great extent.
These people, when they come in contact with the core of the Buddhist philosophy, have an automatic tendency to catch on to it as they see it is the same they have seen in real life by experiencing both worlds (the day to day hardship to achieve the material goodies we all are taught to strive for to get to "happiness" but at the same time realizing that it never brings real happiness, happiness is a state of mind, All phenomena starting from the atom,is in a state of constant change, and where ever there is constant change their is never true and permanent hapiness etc etc ). Due to their state of concision's, they tend to catch on to this faster. If the majority of these people in these so called Developed world happen to be educated Caucasians, well, you can put the "hat" on them.
sam the man