That has nothing to do with the aircraft itself, but the ship it's lauching from. SU-27s and 30s take off from normal runways all the time without the "aid" of a ski ramp. It has to do with the size and length of the carrier. Neither Russia (Soviet Union) nor India has a full length carrier like we do.
I don't disagree with you, but the other thing to think of what mods would be necessary to make the Su-27 and -30 durable enough to endure the rigors of cat launches? Are those mods feasible? Even a "full-size" carrier doesn't compare to a runway.
Incorrect. Although smaller in displacement both the Kuznetsov and the Gorshkov, sold to India and to be recommissioned as the R Vikramaditya, are nearly as long as a Nimitz class boat.