err.... yes.
As a south Indian, with a south Indian wife and living in south India, I do not think I need "gyan" from you about how many south Indian people speak and understand Hindi.
Almost all south Indians are Bilingual, Many are tri lingual and the population that do no understand hindi is very low. Even in TN people tend to understand Hindi, they just do not like to acknowledge it due to language chauvinism.
Its similar to France, where people might understand english, but pretend not to understand english. I have always found it easier to ask them directions in Hindi. That way they go out of the way to help you. Asking them in english only makes them snub you.
Please read my post again before getting your knickers in a twist.
I made the point that hindi knowledge is south india is not through school curriculum. Except CBSE and ICSE schools - which no doubt middle class folks like you would have attended - state board students will not have to learn hindi, and many complete their entire primary education in the local language. This latter group derive their undrstanding from TV, interaction with others.
It's foolish to make a claim that most people who go to school learn hindi from school when what you mean is a tiny fraction of schools. Go to a primary government school in Bellary and see how much hindi they learn there