Wow, what a giant topic. I can only speak from observation, and not legally at all. In my college days, it seemed that there was still a sense that, if a woman dressed or behaved "a cerain way" she "wanted" it, and so was fair game and no matter what happened, it was assumed she brought it on herself. This reflected and placed a responsibility on the part of women, for the behavior of men that women now resent.
The flip side is that women now dress as provocatively as they chose and/or tease desire from men, then call it rape when it goes further than they are comfortable with the next morning. Women may feel more powerful or attractive for having attracted a powerful man, a notch on the bedpost, so to speak that some may later try to parlay into the power to control, extract from, or if all else fails, ruin. Miss Lewinsky, and Ms Tripp come to mind, while though consensual, was still used to harm.
As many married men will know, many women have learned to exercise their power by giving, and with-holding sex. Taking
sex from them then, is theft. Just as the getting of it by distorting
the truth, is a con. I don't know that anyone can understand the nature of attraction, and wanting to be attractive, of desire and wanting to be desirable, of acceptance and wanting to be accepted, and not also recognize that any of these emotions make us able to, and vulnerable to manipulation and one-sided encounters.
I think all of the examples you gave were one-sided encounters, based on the needs of one, and perhaps the vulnerability of another-with or without force. While it may or may not have been rape-if rape is defined by the use of overwhelming force used by one, to subdue another person for the pleasure of one-consensual sex under false pretenses of trust, acceptance, or entrapment might in the morning not feel as good as the idea of it was the night before, might be as harmful to some emotionally, as to others physically.
Many believe that it is the consequent emotional damage that is caused by the use of overwhelming force, the power that leaves others without a voice and without control that is rape. By this broad definition, the powerless often feel raped by the powerful, even if sex is not the means.
So when is it sex? Safely I think it is sex when it is between people who have developed, and plan to continue a relationship. Whether it turns out to be for better or worse, the effort at a relationship built on respect for mutual understanding is what makes it sex. In this view, I think there is a place for legalized, I'll call them "escorts," because both parties have a clear understanding of what is expected. Fee for service, so to speak, makes it a business arrangement, rather than an emotional entanglement.
The view of extra-marital sex in this country would be different, as it was in times past when marriage was much more difficult to end, if it didn't so easily lead to divorce, and family dissolution. The woman as single parent, breadwinner has proven ineffective for the woman and children, while the man keeps his bread winning capacity and gains freedom from responsibility. I again hold that extra-marital sex might be and alternative for both men and women who find they want more sex than they get at home, but don't want to break up the family. Of course, children might result from this, as it did with "the Terminator." and what to do about that is a problem too.
So, in the end, I've talked myself into believing that the consequences of sex outside of a committed relationship are often damaging enough in their power to do harm, as rape is, and therefore might be considered a different kind of rape, but a rape of the family and the children who suffer the consequences of it.