Having been happily married for 10 years and a father of two kids (11 and 10) I can definitely see how married life not only makes sex more difficult and reduces the opportunities for it, but also how it reduces the females desire for it.
Early in a relationship when everything is exciting and new, naturally both parties want to have sex frequently. However, once a relationship becomes a stable, long term affair or a marriage, the woman no longer feels like she needs to impress the man or try to keep him around with lots of sex. It's not a conscious decision, mind you, just a result of evolutionary biology. On the flip side, nothing changes from the man's point of view regarding sex: he still wants it all the time, save for the uncommon cases when a male becomes low desire.
My wife and I have had many discussions about sex and our fair share of arguments, too. For her, stress, being tired, not feeling attractive, and the kids being awake all detract from her sex drive. To top things off, she's been on birth control for many years and it, too, reduces her libido. She rarely turns me down for sex and I try to temper how often I initiate so as not to set myself up for disappointment too often. That being said, we still average around 2 times per week. It used to be 1 until I decided that as my 35th birthday approaches there will be a day when my desire will wane and I want to take full advantage of it now while I still can and she's been OK with that. Our biggest issue now is that I'd like her to initiate more often and she's been improving on that front. I'm hoping now that I'm snipped she can go on a lower dose of hormonal BC to help get her libido up plus I've been doing more laundry and chores around the house so she doesn't need to worry about them so much. As I told her, you're not my sex slave and it's not fair to expect you to have a busy day at work, come home and do chores, then be ready and willing once bed time rolls around.
Ironically, we went through a period of the exact opposite ~9-10 years ago and I didn't even realize it. I was big into jerking off to porn and it reduced my libido while hers was high. I could have been having sex a lot more often then but was too stupid to realize it. Looking back on it, I really kick myself. My wife will be 31 this year and I'm really, really looking forward to her hitting her sexual peak in her 30's.
In this guy's case, I could see how compiling a list of rejections might be eye opening to a spouse if presented to her calmly and in private, but not sent over email accompanied with vitriol and followed up with the silent treatment. It just goes to show how poorly they communicate with each other and how unhealthy their marriage is.
Over the years I've learned sex is a two way street. As a husband who desires lots of sex, until someone invents a horny switch that can be installed in wives, if I want her drive to increase there's things I can do to facilitate that whether it be doing a better job of setting the mood or just taking a load off of her so stress or worry don't get in the way. To get me started, I'm like a push button ignition -- just hit the button and the engine starts. For women, many are like a stubborn engine that requires some extra cranking to get going. That's not a bad thing, it's just the difference between the sexes. My wife does awesome things for me that she may not be interested in because she truly loves me and wants me to be happy. When it comes to sex, why should I be exempt from doing the same for her?