It kinda does, merely drinking doesn't make you unable to give consent, you'd have to reach the point of intoxication where you were incapable of consenting. Alcohol loosens inhibitions, but that alone doesn't make you incapable of consenting, merely more likely to consent (and maybe regret it the next morning).
The problem isn't the line, but the burden of proof in determining how intoxicated the person was, and that judgement tends to be subjective (since rarely do you get to take the victim's blood alcohol during the evening, so observed behavior is all you have to go on).
From the transcript, the girl did not engage in behaviors that would suggest severe intoxication (falling down, slurring, lack of awareness of where she was or what she was doing, etc.).
The problem for the prosecutor is the "beyond a reasonable doubt" standard, without strong evidence that she was incapacitated, or a witness to her telling someone she wanted the night's activities to stop, it's almost impossible to convict.
A civil suit merely needs a preponderance of the evidence, which is why you often see it in these cases. Ariaza seems like a tough case even for this standard, but he may have been added merely because of perceived "deep pockets." Winning civil suits against defendants with no money doesn't pay a lawyer's bills.
