Why do women orgasm during rape?

I think that the answer to the question as to why do some females orgasm during a sexual assault or rape is that all of the various explanations have some validity, but none of them tell the entire story in the case of every individual victim of the crime. 

First of all, orgasms in women being raped are not frequent, but they are not uncommon either. In the study you cite, about 5% to 21% of women interviewed in the studies surveyed reported having an orgasm when they were raped. Researchers have hypothesized that the actual figure is probably a bit higher in reality due to victims being understandably embarrassed both by the rape and by having achieved an orgasm during unwanted, forced sexual relations. Around 20% seems to be a likely, real-word figure. 

Why would almost 1 in 5 women have an orgasm during the rape? Conditions probably have to be right. What you mentioned about long enough stimulation of the erogenous zones is probably often correct, because most women unless highly aroused prior to penetration don't orgasm quickly during the act and the man is likely to finish before she has had a chance to have an orgasm. So it is likely that in some case the rapist engaged in various kinds of foreplay during the assault. But, at least 20% of women like me have a highly sensitive g-spot and achieve orgasm during intercourse very frequently and fairly easily at times. That might explain why some women might orgasm even during a short violent rape. In fact in one study even several women who were beaten up during the rape still had orgasms just from intercourse. I would think that they also had to be women with an active G-spot. 

It also might be that physiological and adrenaline response that you see often referred to in some articles too. But other researchers question whether a woman can really have an orgasm unless at some point she wants the orgasm to take place in some part of her mind at least. They say that women just cannot have an orgasm unless she concentrates on it a bit. If this is true, is it because of our biological heritage from cave man times like you wonder? Perhaps it is for some women at least. Although we now live in civil society (at least in the developed world) humans were hunter/gatherers and cave dwellers for a far longer part of our history than they have been civilized. Our thousands of years long history as cave dwellers and hunters can't be erased in our genes and predispositions after only about 5000 years of civilization. Some women probably do at some unconscious level respond to a man taking control of her physically and having sex with her by dominating her physically even to the point of responding in the extreme case like during a rape. Many women engage in play with their bf's or husbands which are like a play or role played rape in some manner, so it obviously again something that just turns some women on. 

Altogether, it is just a fact that some of us will orgasm during a rape. The explanation is complex, but the bottom line is that whether or not a woman orgasms, if she is raped it is an experience that will haunt her unless she receives support, counseling and understanding in order to deal with the complex and deep emotions caused by the experience.