*shakes head*
Can Ken juggle from an air-to-air MP in Street Fighter? Can Ryu's crouching MK in Third Strike stand up to Ken's in the same game?
Not to mention that Ryu's more of a power character who capitalizes on your mistakes while Ken is more about flash, and depending on the game, is more about combos.
I'd write a more detailed analysis but don't have time right now. Let's just say they did start out the same at first, but became radically different the farther the series went.