Actually I thought your gravity analogy was more thought provoking.
We do all wear uniforms that is certainly true. And there are some behaviours that are more common to some categories of people than others. But is class, with its three main designations an adequate descriptor for these many differences, what about National Statistics Socio-economic Classification :
1.Higher managerial and professional occupations
2.Lower managerial and professional occupations
3.Intermediate occupations (clerical, sales, service)
4.Small employers and own account workers
5.Lower supervisory and technical occupations
6.Semi-routine occupations
7.Routine occupations
8.Never worked and long-term unemployed
http://en.wikipedia.org/wiki/National_Statistics_Socio-economic_Classification