As in much else, India is extremely diverse when it comes to languages as well. While Hindi is the most spoken language in the country, it is by no means as prevalent as North Indians might think. Especially in the south, a substantial amount of people do not understand or speak Hindi at all. That goes for all levels of society including the educated.
The map above only shows languages that had more than 10,000 million speakers in the 2001 census and its geographic distribution is not exact with all of them.
Just to give you an example, on one of my recent train rides, I was chatting away with three of my fellow passengers. Two were from Madhya Pradesh and one was from Tamil Nadu, which is in the south. Among many things we discussed, we touched upon language and to my big surprise, the guy from Tamil Nadu did not speak Hindi at all, even though he was highly educated and frequented Agra to conduct business.