It's bit surprising, It's for the first time I have noticed, Diwali is celebrated on two different dates - Saturday in Kerala and Tamil Nadu, and Sunday for rest of India. I think North Indians and south Indians follow different calendars and a Hindi month starts 3-5 days prior to Malayalam/South Indian calender. That's the reason why Janmashtami may be celebrated almost one month difference in North and south, as it's purely based on stars falling on a particular month. If South Indians follow the same calander, why Diwali is celebrated on Saturday in Kerala and TN, and on Sunday in Andhra Pradesh?
Like it on Facebook, +1 on Google, Tweet it or share this question on other bookmarking websites.