Each one has a logic for naming. There is one group of principled people whose only principle is to find a name that can't be easily pronounced by all. If the number of people that are able to pronounce it correctly is more than that of those that can't, it is a failure for that name. Some others say, whatever be the starting, whatever be the ending, it must have 'sh' somewhere. Another group of people look for names based on the birth star. Only the first letter is important and the rest could be compromised. Another group looks based on numerology where every letter counts. Each letter is given a number and the sum of all those numbers should be some specific number. Some people want to prove their kid's uniqueness through the name by keeping a name that nobody has ever had. Some people choose names that are heard often in their surroundings. Some people are busy filing applications to change their original names in gazette.
There is another group of people who are very clear about it right from childhood. For them, whatever it is, it should be a movie actor or actress's name. A subset of them is very clear about which actor's name it should be as well. Some are slightly different. They choose their names from movie characters. Some want to have names from epics, literature, popular novels, etc. Some want to keep only god or goddess's names. Some people have been having the grandparents' names for many generations. It will be the same two names that continue for generations. A's son is B, B's son is A, A's son is again B, and so on. Some people keep names of revolutionists and popular leaders that worked for the people. This is prevalent in any culture that goes through a phase of political transition or revolution. In Indian context, it happened during the freedom struggle movements. People in political parties use this opportunity to please their leaders. They go to their leaders to get their kids named. The leaders suggest their own parents' names, pets' names, etc. and please their followers.
Some people go with their girl friend or boy friend's name if their love didn't succeed. Some keep their bosom friend's name. There are some people who are adamant about one thing while deciding a name. Their only condition is, that name should not have any meaning in any language. They just concatenate few letters. One of them letters would be 'J' mostly. Some just go with names that are most heard in news and current affairs when the baby is born. So, there are many such categories and the list is not complete.
Even in my house, you could see that all our names were influenced by one of the above phenomenons. Since my grandfather was a freedom fighter, he brought home all his inspirations in the next two generations. Starting from Subhash Chandra Bose and Bhagath Singh, we have all sorts of names including some local Communist leaders. As a family that ran into many troubles because of this strange naming convention, I would like to have a quick discussion around it today. The most affected of them all is Bhagath Singh, I guess. To make matters worse, he looks like a North Indian, too. :)
You would be surprised to see the number of Boses in some parts of Tamil Nadu. It is as common as Senthils and Saravanans. All their fathers or grandfathers would have been ardent followers of Subhash Chandra Bose. You would have seen this in the movie 'Indian' ('Hindustani' in Hindi). The old Kamal Hassan is a freedom fighter and his son young Kamal's name is Bose. There is no dearth of Gandhis, Nehrus and Tagores as well.
So, when our North Indian friends hear these names in South India, it would sound very funny to them. I know, it is as funny as a North Indian having his name as Kamaraj Nadar, Deve Gowda, Chandrababu Naidu or Krishna Menon. Comparatively, this is more in Tamil Nadu than in any other South Indian state. That is where surname is a completely extinct concept.
It was all fine till the last generation. Because, people mostly didn't come out. Only the affluent families sent their kids outside for studies and jobs. So, those names were used only within a village or town. People would have exclaimed, "Wow, what a novel name?!" and boosted their pride. Even the holders of those names would have felt very proud about their names and thanked their parents. But, things have changed now. Our current generation boys and girls go all around the world. They go through a lot of teasing and become a laughing stock. Though they laugh with others, it indirectly affects their self-respect also. I personally know some people who go through such painful experiences. There are some others who don't even realize that they are being made fun of. They just take it as a compliment and move on. :)
So, my request to my South Indian friends (especially the Tamil friends) is - Never allow anyone around you to copy someone else's surname for any reason whatsoever. We have got rid of our surnames long back. It's time we start doing it with other surnames. If you love someone so much, please take their first name. Taking just the first name doesn't reduce the degree of admiration or love.
And, to my North Indian friends - If you ever come across someone with such confusing surname, it may not mean that they migrated from some part of North India to South India or you don't have to be puzzled about the reason why they use someone else's surname. It was just a symbol of their pure love or admiration for someone that doesn't belong to the same land of theirs. And, we actually don't care too much about surnames. Not sure if it is one step ahead or otherwise. :)
Post Script (A later addition based on Sahana's suggestion): How did I get my name - Bharathiraja Ramachandrabose? I am Bharathiraja and Ramachandrabose is my father. How did I get my first name? I was named after the popular Tamil poet and freedom fighter Subramanya Bharathy (They call him the South Indian Tagore!) - as Suresh Bharathy. This was done by my grandfather, who was a freedom fighter and an ardent follower of Bharathy. But, my father later changed it to Bharathiraja from Suresh Bharathy. In any case, just 'Bharathi' sounds girlish, I guess (My friends call me 'Bharathi' and those who haven't interacted with me think I am a girl until they meet me and get disappointed looking at a tall, dark and handsome boy with a girl's name when they meet me!). An additional info - Subramanya Bharathy's native place and mine are very near. It was walkable at 'that time'. How did my father get his name? Subhash Chandra Bose was my grandfather's inspiration. I have heard that his first involvement in the movement was when Netaji was in Madurai for a demonstration during his school days. And, when my father was born the freedom movement was in its peak. It was 1942. As I had mentioned somewhere, he also did a mix and match with his father's name and leader's name and named his son Ramachandrabose (Rama from his father's name and Chandrabose from his leader's name!). So, in our chain, my grandfather was the last one to use our surname and I would be the last one to use someone else's surname. Unlike my father or my cousin Bhagath Singh, my first name itself doesn't contain a surname (though Raja is a very common surname in Rajapalayam - a town in my region - the town of Rajas - Rajas' palayam!). So, my cousin Bhagath Singh will have to bear it for another generation. His kids would be called Nivedita Bhagath Singh and Naren Bhagath Singh. :)