1: Hormonally, sex is a LOT more important to men than it is to women. The chemicals in our body simply do not allow for any other thought than just sex, really,ESPECIALLY in the teenage years of puberty.
2: I'm assuming that you heard or read about this in a sort of census or test that took an average of all the times guys think about sex and divided it by the amount of minutes in a year. Startlingly enough, in that respect, guys SHOULD on average think about sex at least once every other minute. However, its an average, and therefore, totally biased. Think about it; I read once somewhere that a baby is born in the world every minute. Highly believable,considering the population of people in the world, the population of women, the population of pregnant women, and all the babies born everyday, it seems plausible, no? Well, not entirely. You don't think that every now and then a baby ISN'T born every minute? Same thing in this case. Men don't think about sex frequently, but we don't think about sex infrequently, if you get me.
3: There's a big difference between thinking of sex and just thinking about... um... sex... (Hear me out, please.) If a guy ogles a women he passes in the street, he's not necessary thinking about having sex with her. He could be thinking about one specific part of her body (probably the part he's staring at) without thinking about sex as a whole.
Oh, god. In writing this, I realize how disgusting this all sounds. That's the male mind, for you. I apologize if I offended anyone. Just throwing out more two cents.