He took Salman Khan's name because he's starring in Prem Ratan Dhan Paayo.
Anyways I wouldn't want Salman signing this remake as too much of similarities (fighting for the needy, finding self worth in helping/fighting for others) in the films he has been doing. And to cast him, they've to wait till 2017 which again would become too late for a film like this.
Aamir Khan, well he suits the role too but the role of "Kaththi aka Kaththiresan" is something we associate with Salman or Akshay Kumar. Even Ajay Devgn but audience won't accept it in a big way like it should be accepted.