India and China are vast countries, the diversity should also take into account population/area of the country on which limits are enforced.
http://travel.state.gov/content/visas/english/law-and-policy...
In practice, someone from Iceland or Tuvalu can get an EB (category 2) visa in about a year, whereas the average for someone from India or China is more like 5-6 years [2].
[1] http://www.uscis.gov/tools/glossary/country-limit
[2] These rough numbers are from observations on http://www.trackitt.com, where applicants self-report application statistics
It is not clear to me how having a diverse country that is not dominated by immigrants from one or two ethnicities arrives from letting this happen. Or how it is fair to the guy from random tiny country X when he has to compete against two largest sources of immigrants to this country.
Compete for what?