I think it's just ingrained in us - women seek strong men, concsiously or not, and the most obvious outward sign of this is size (even though a guy who is shorter may well be physically more powerful than a taller guy).
At 5'7", I'm definitely not tall - I've dated women taller and shorter than me; my wife is 5'6". I think she figures as long as I can toss her around in our matrimonial relations, she's happy.
