Quoting MPT: The point is, however, that the book is going to tell your wife that she's the one who is going to have to give the most, put the most effort into changing things because she determines how often sex occurs.
Well, think of it this way. In a relationship, if one person "wants" something from the other person, and if there's nothing stopping the other person from giving it to them, it should be given. IE, if I want a kiss, and there's no reason for my wife to not give me one, she should give me a kiss.
Of course 100% of the time is not needed, but in general, if a spouse feels a need for something from the other spouse, the other spouse should provide it.
The same thing with sex. If spouse1 feels the need for sex, and spouse2 doesn't provide it, spouse2 is the one who needs to change. We don't say "I don't feel a need for kissing like you do, so you better get used to no kisses". No, we just kiss our spouse when they want kisses, even if we don't need one at the same time.
I think people just view sex as such a huge ordeal that they feel they have the right to refuse it if they're not "into" it. That's one big thing the SSM book hits on really well.. it doesn't matter if you're not into it, it's one of your jobs as a spouse to do your best to give your spouse what they need. Even if you don't feel like sex, you should have sex anyway.
So I think it's perfectly natural for a relationship book to say that the person who's Not giving, is the person who needs to work on things.