comparatives - "than do I" vs. "than I do"

I need grammatical explanations for the following two sentence structures:

1. The mistakes children make in learning to speak tell linguists more about how children learn language than do the correct forms they use.


2. Freedman's survey showed that people living in small towns and rural areas consider themselves no happier than do people living in big cities.

If noticed, would someone explain me why "do" appears after "than" in the both of the sentences above?

So, would it be correct if I say, "You explain it more clearly than do I"?