Everyone cannot do all roles and some roles and stories fall in the laps of particular stars and they turn out to be evergreen classics and blockbusters. Versatile stars are required for films taken in special genres and it is not enough for the stars to have sensational fan following in crores.
Shankar actually penned Indian story keeping Super Star Rajinikanth in mind. However Rajini was in two minds as he did not have call sheets then and also one of the roles was of an old man. The story finally went to Kamal Haasan and the rest is history.
At one point, Shankar even thought of casting Rajasekhar in dad's role and either Venkatesh and Nagarjuna in son's role. But it did not materialize and later he planned to cast Satyaraj and Karthik for the roles.
But with no one coming forward, Kamal Haasan took the bold step and created a sensation with his powerful fight against corruption. Now everyone says that had Rajini did the role, he wouldn't have created such powerful impact.
Similarly one cannot imagine Kamal in Rajini's Baasha, Balakrishna in Kamal's Sagara Sangamam, Nagarjuna in Kamal's Vichitra Sodarulu. Rajini himself openly admitted that he wouldn't have done justice to Indian role like Kamal.