I believe once you get out and experiance the real world you'll realise its simply a generalisation you are making as ive seen friends who are in relationship with just very nice guys who arn't the rough around the edges sort or the alpha male but are quietly confident people, esepcially in this current generation its becoming more common for girls to be as strong and commanding as the males ...
people are too complex that you can't make a fleeting statement like "girls choose ass holes" yeh sure it does happen and where i live i see many girls falling for the yuppies, the guys with the sports cars and money, so they are after the security ..some girls want the loud alpha male because they see it as being taken on an adventure, some girls can't decide so they jump from boyfriend to boyfriend in a short time, it depends on what they are attracted to ..
my advice is to just stop thinking about it because it'll do your head in especially if you are single, just be yourself and immerse yourself in your hobbies and interests and by living the way you want girls will be attracted to your self-confidence ..
some girls like quiet guys too ...
once you stop obsessing you'll also be more inclined to approach and talk without thinking "does she like me, or not, am i saying the right thing" .. etc