U know what, talent is really not necessary, it's an art which comes with practice, watch AB Jr in Sarkar, he is actually decent, watch some of his first movies, he is pathetic. Also see Ajay Devgan's first few movies, he was dumb as a donkey, but then look at omkara, If you are a star son, u are given enuf oppurtunities to learn, Also look at SRKs initial roles, they were path breaking, Darr, Anjaam, that is probably the difference between star sons and self made ppl
P.S : These days both of them suck. I am a fan of niether