Its basic human instinct. We are prewired to pay more attention to the more attractive girl. Been that way since the first caveman picked the hot chick to hit over the head and left the ugly one alone, it aint changing any time soon. Of course the guy at the gym will through on a couple extra plates and act like he can lift more if a hot girls around. Whats he doing at the gym in the first place? Hes getting in better shape to impress the ladies so he can land the hot one.
By the way SHE'S HOT.