This isn't news to a lot of women. I know some girls that put out even when it hurts them. In fact, a lot of girls do this, because they understand the point I am about to make. Granted, some do it purely out of subjugation or fear of their man, and this probably isn't healthy. But others do it willingly, and they are smart women.
The practical side of this argument is simple. If a man is aroused enough to want sex, he can probably be finished in 15 minutes, so not having the time is a poor excuse. And with all of the lubricants available, equally poor are excuses about "not being in the mood." But the practical reasons aren't usually the important ones. More than likely, you refuse because you don't want to make the emotional or mental effort necessary to get into a sexual state of mind - and I don't suggest that doing so is easy. If it were, this post wouldn't be necessary. However, neither is it easy for your man to put down his work to listen to you vent about your bitchy coworker, remain emotionally stable in difficult times, lead and support the family, etc. - all of which are the kind of things most women want and even expect from a man. In a good relationship, women and men both make sacrifices to give the other what they want - and men want sex.
To put this in perspective, consider the following. Men are largely independent, and don't seek the same things from a relationship that women do. While men love your radiance, your light-heartedness and your femininity, we don't crave these things anywhere near as deeply as we crave your body. Saying no to your man when he wants sex is analagous to him saying no to you when you look to him for emotional stability, direction, comfort or protection: though it is not the only reason he is attracted to you, it is the primary one. Sex is the one thing he wants most deeply but cannot provide for himself. I don't mean that women exist solely for a man's sexual satisfaction; but I do mean that his sexual satisfaction is critical to his happiness (more so than a woman's is to hers) and that you hold the key to that satisfaction.
A woman who attends to her man's sexual needs is like a man who attends to his woman's emotional ones. Conversely, a woman who neglects her man's sexual needs is like a man who neglects his woman's emotional ones. Think about that for a minute. It means that the equivalent of a woman who slips into lingerie at the end of a long, exhausting day because she can tell her husband is in the mood, is a guy who turns off the TV and listens to you when you need to talk, or drops everything to hold you when you need affection. It means that the woman who Googles "how to give a great blowjob" or tries to learn what her man likes best in bed is like the man who reads a book on understanding the female mind, or makes an effort to understand what you need most when you are in different moods. It means that a woman who refuses sex because she is angry with her husband is like a man who intentionally refrains from stepping in to deal with the asshole car salesman that is trying to rip you off, because he is still annoyed about the argument you had with him earlier that day.
Yes, men also have some emotional needs and appreciate a woman who understands them - just like a woman has sexual needs that want satisfying. But a man's sexual needs are his priority just like a woman's emotional needs are hers. (Obviously there are exceptions to this rule, but I am speaking in general terms.)
So break out the silicone and lingerie and tune up your acting skills. And the next time you struggle to get in the mood, remember how much you appreciate or want his efforts to support you emotionally. Better yet, anticipate his sexual desire and initiate it yourself, just like you want him to anticipate your emotional desires and provide the affection or companionship you want, without having to ask for it.