As Angus points out, murdering Hutus had been a Tutsi sport for centuries with the occassional genocide occurring something like twice a century before the hutus rose up in 1994. I thought the main reason for the number of women was that so many men were killed, but that was a pure guess from me.
In Rwanda, the Hutus rose up much earlier, in 1959, and proceeded to murder the Tutsi in turn afterwards, until they were defeated in 1994 by the RPF (who still rules today).
Of course, down south in Burundi, the Tutsi stayed in power and kept up their own massacres of Hutu, ending...err, this year I think.
Two sides of a bloody looking-glass...