I was asked if common sense and horse sense were interchangeable.  I answered:

They have the same meaning, but "horse sense" is more "folksy".  It's more informal.  I'm sure it's heard more in the country than in the city.

Was my answer too vague?  In my reply I said that (1) the two expressions have the same meaning, (2) but "horse sense" is more "folksy" and informal.  I don't know a way to make part (1) any clearer.  Common sense = Horse sense.  In (2), the second part, I was referring to the usage.  "Horse sense" is informal, something that can be expected to be heard more often in the country.  Would President Obama use it?  Sure, why not?  But I would expect to hear him use it when he is trying to sound informal, "one of the masses".