Although the legal definition of rape is very clear, I agree that there are different degrees of rape wrt the experience of being raped. I have never been raped by a stranger but imagine that must be the worst possible context. In my own experience, being forced to have sex with a partner when I was ill was much worse than being forced when I was not ill.
But I don't really see why it is helpful to draw attention to the differences in degree though, given so many women minimise what has happened to them anyway. I recently watched the film 'the Girl with the Dragon Tattoo' and found myself watching the very brutal rape scenes in that thinking 'well, what have I got to complain about, nothing as traumatic as that has ever happened to me.' 
I am surprised at the comment from Rape Crisis about rape being the worst thing that can happen. Being raped by a partner certainly wasn't the worst thing that has happened to me. In fact the worst thing that this partner did to me sexually wasn't actually something that is officially classed as rape anyway. (And for ages after that I thought 'well, it wasn't rape, so why has it upset me so much he did that against my will?')
I am also surprised at the comment from Rape Crisis that 'it is going to affect women in exactly the same way'. I have certainly been affected by the time that I spent in such a crap relationship, but I find it hard to believe that I will have been affected in 'exactly the same way' as someone raped by a stranger in a dark alley.
Maybe it is just that the woman from Rape Crisis has been somehow taken out of context or misquoted.