In Canada, there is certainly a point where intoxication makes people unable to legally consent. Presumably the police and/or prosecutors felt there was not sufficient evidence of that level of intoxication.
[1] “because he is easily recognizable in a photograph showing him raping the victim while she is visibly ill… why the RCMP decided these photographs aren’t evidence of rape is beyond us.” http://www.salon.com/2013/04/12/anonymous_on_rehtaeh_parsons...
I'm not saying that Rehtaeh Parsons was not raped; only that when the police and prosecutors say that they do not think they could secure a conviction, I'm inclined to trust their expertise and knowledge of the case.