Not true. You may feel tough communicating with Tamil people in Chennai. But u can still use English or sign language. They would be happy to help. People in Chennai usually don't say you need to know Tamil to be in TamilNadu. They know you are outsider. They are tolerant. But you need have the same tolerance when they cant speak Hindi. The real problem comes when you tell them to talk in Hindi or get pissed off if they refuse to talk in Hindi. You can still survive with good English in TN major cities.