20,000 for phd including post doc is big number.  I dont think usa will produce such a big number of phd graduates.  it does nt matter even if they are exempted from quota system.  i think number for undergrad should be increased to 50,000 masters to 30,000 and phds are exempted from quota.  just my thought.  this issue need some research though regarding how many quota should be added.  rest of the world, 20,000 is good enough.