The mechanics of sex, which is arousal and passion, are very easy for a man even with little or no emotional connection. Such as the expression men are visual, this is only a half truth, as both men and women are visual, but the man can be stimulated sexually very quickly again, before there is the emotional component. This is why images of pornography is so stimulating and causing such a sexual reaction to a man.
A woman is surely as visual, but will react far stronger sexually after the emotional component is present. For the woman, this comes from how she feels about a particular man, is he dominant, confident, is he protective of her, does he respect her, does he deserve her intimacy and openess? If the answers to the questions are yes, the woman will often then react very strongly sexually. Notice this can happen very quickly, as quickly as the woman will form an opinion on the man. Regardless, in this way, it can be assumed there is more situational depth required for a woman to be fully sexually excited. This is why a woman is not so engaged by images of pornography as a man.
But a man, after the act of sex, will certainly have very deep emotions, stemming from primal urges to protect that which he desires. I will argue that a man can be every bit as emotoinal attached as a component of a sexual relationship, it just tends to be more apparent after the fact, and again the emotional attachment is not necessary for the initial sexual arousal.
A very good question.
I believe it is important to understand because men and woman experience sexual and emotional feelings in a different scheme of order, it doesn't mean that the man or the woman does not have both components, and that both are valid.
Women are very much sexual creatures, and men are very much emotional creatures!