I think date rape is the same as stranger rape, assuming the date rape is a rape when the two people have never had sex before. But, rape when the people are in a current relationship and have a sexual relationship is a little different in my mind. It is still rape to me, but most likely in that situation the woman is not terrified she might be killed, unless her husband is abusive all around, which is likely the case, and then there are all sorts of problems, criminal problems. Some women might feel raped just because they went along with sex with their boyfriend when they did not feel like it, and they said no, but still kind of went along. He should have stopped, but maybe he did not take her seriously enough and would have stopped if she was more adamant. He is still wrong, she should not have to say no twice, but when two people have a long term sexual relationship their body sort of becomes your body. I find woman vary vastly on whether they feel sexually abused or raped and whether it persists as an every day part of their psyche. If I had sex with my husband when I was not really wanting to, if I had been emotionally moving away from, and had no desire to be physical with him, if he kind of got me to have sex, even though I voiced I did not want to, I think afterwards I would cry, and feel used, maybe dirty, but I would not feel he deserved criminal punishment.
The law cares about punishing, but it also cares about societies safety. Serial rapists lurking in parking lots are a bigger problem to society at large than the one asshole criminal violen rapist boyfriend. If the law has to prioritize, then protecting the many would be the priority.