There is controversy over how much ADD is a 'culture bound' syndrome that is particular to the US (though gaining ground in other nations such as Canada, the UK, Australasia etc admittedly).

One thought is that it has more to do with the pathologizing of a spectrum that is more appropriately thought of as being within normal range. There are individual differences in such things as ability to focus attention etc, you see. Not sure on the prevalence of ADD... Guess if you fall however many standard deviations below the mean (or you or someone else kicks up a fuss about it) then hey presto you get to have ADD and stimulant medication to improve your attentional focus / control. At least... In the short term (before habituation).

Dopamine, yup.