I'll try because I've really thought about this one but I don't know if it will make sense.
In one scenario she might be hinting for you to get ready to be jumpable (i.e., take a shower, brush your teeth, use mouthwash, etc.)
Secondly, we may not actually WANT sex in the classic, down and dirty state of "Being Horny." But we are trying to tell you "Could you get my motor started because I'm NOT horny but I want to be with you."
And yes, I know this sounds really weird.
If we WANT sex (i.e., are actively horny, which for some women only happens for about one week a month) the vast majority of women will generally be quite direct. We know where your dick is, we know how to grab it/suck it/jump on top of it. The problems start when we want to be affectionate and want that contact but are not actively horny. If we try to get things started when we're like that guys are NOT stupid and they misunderstand. They know our heart (or anything else) isn't into it, and then things get weird and fights can ensue.
This is really fucking hard to explain in writing.
Look, men, trust me, if your wife has key phrases or sounds or touches she uses to signal her willingness, just go with it. She's asking you to start her motor so she can jump your bones.
If this makes no sense I'm sorry ...