that's because you don't hear about most rapes. most rapes are never reported.
What can we do to increase reporting? Obviously the social stigma, even in western "civilized" societies, keeps many from reporting, as does, I'm sure the justice system, which until very recently has often been perceived as permitting the rapist to put the victim on trial for the way she "looked" or "dressed" or "walked" or "spoke".
While I agree that some rapes probably go unreported, I'm not sure how one keeps statistics on matters unreported.