men taking advantage of very drunk women isn't really that peculiar, happens all the time, the only unusual thing is that someone actually got convicted for it. I imagine the spiking theory came because she was obviously blackout drunk and probably didn't think she'd had enough for that to be the case, or maybe she was spiked previously.
Reporter I work with said was at a rape case once and jury had cleared the defendant, then after the verdict the court reads out previous convictions (they are not usually made public so as not to bias the trial) and they were a string of sex assaults etc, half the jury broke down in tears apparently.