Ok, wow, this thread is hard for me in many respects. I'll provide my take and hopefully it helps.
I've read the whole thread, and I'm still not 100% sure what you mean by "on demand sex." Can you give us an example or two, in your own words?
For me, I felt pressured to have sex for most of my marriage. Our drives weren't mismatched; our emotional needs were. I felt emotionally unfulfilled and shut down over time.
My WS never called me names. He just wouldn't speak to me. For days. Or even worse, he would stroll right by me, not look at me, with an angry countenance, then smilingly greet one of our kids. Do you have any idea how hard that was for someone whose love language is quality time? I was dying inside.
I lived with what I mentally referred to as the Anger Fire Hydrant, seething in my living room, waiting to go off. My transgression? I'd said no to sex the night before. Why? Who knows. Sometimes I was exhausted. I'm the primary income earner, and guess what? I was also the primary parent with our kids. Other times it was timing. Female hormones can be a mercurial thing that even we don't fully understand.
A typical scenario for us was that I'd wake up really early, do most of the work to get the kids ready (we have three), we'd both help drop them off at school or daycare; we'd both work; I would pick the kids up, make them dinner, baths, homework, read to them, then bed. My WH would do the dishes and fall asleep on the couch while I did the above. Then I would crawl into bed at 10, wanting to crash; he'd be wide awake and eagerly follow me to bed, ready and raring to go.
Yes, he was (and is) very willing to also take care of my base physical needs. But foreplay? Nope, what's that? Kissing? Who the hell needs that. Let's just go straight to the goods. I felt like I had two body parts (three, if you consider each of the girls a unique object). But why is she complaining, she got off, didn't she? Yes, if you count half a step above taking care of it myself.
I wouldn't always tell him I was exhausted, but he knew for years (after telling him many many times) that I was a morning or day gal. But nope. He was a night time guy, so with the night came the pressure. I'd be half asleep, he'd start pawing, I'd feel guilty some nights and give in; other nights I'd say no. And when I did say no? Oh boy did I ever pay. For days. Please refer to "seething anger fire hydrant" above. And who the hell wants to be intimate with an angry person? How Not To Get Your Wife In The Mood (by HPV, on Amazon, see $1 kindle section).
Was this "sex on demand"? Who knows, I'm still not sure. But I will tell you how "sex under pressure" feels. I felt used. I felt unappreciated and unimportant. I felt lonely. I felt all my passion was unwanted: who needs quality when quantity is clearly so much more important? So I stopped trying to be passionate during sex. I gave up.
Guess what, guys? Oftentimes for women, once the emotional needs are met, the sex follows naturally. We learned that valuable gem in MC, and it seriously worked for us. Post Dday, he's tried hard to stop stonewalling and the angry silent treatment; he started being much more considerate of my feelings and emotional needs, and guess what? My husband was floored. He had no idea how passionate and great sex could be. Both the quantity and quality skyrocketed. We're both very happy with it now.
To those of you guys who feel angry and entitled: Good luck with that. Hang onto that anger. Pressure away at your spouse. But you have NO IDEA what you may be missing.