All rape is sexual assault. Not all sexual assault is rape.
Rape is a specific violent, damaging, traumatizing act done by Men with their penises to Women (i.e., Females, the people with with Female reproductive organs).
Rape is terrible. Sexual assault is terrible.
A MAN penetrating a WOMAN with his dick when SHE DOESN’T WANT IT – that is rape.
You think I just don't understand, but I don't believe you. 
So a man penetrating another man, a man penetrating a boy, a man penetraring a trans woman (all of that with no consent whatsoever) are all NOT rape?
Trans women are men. All of that is sexual assault, and all of those things are horrible.
TW for discussion of what constitutes rape & sexual assault, and for discussion of consequences of both.
Rape as a term is legally defined – it doesn’t have an intrinsic meaning that transcends cultural, legal, political and linguistic boundaries.
Where I live (the UK) rape is a statutory crime. It’s legally defined as the penetration of the mouth, vagina or anus. The gender of the victim is irrelevant.
Of course, where I live your kind of transphobia is becoming far less common. So, while many people in the UK still exhibit transphobic attitudes, we now have legally enshrined protection for trans* people, legislation that recognises every person’s right to self determination, and laws which protect minorities from abuse, discrimination, hate crime and prejudice.
Our rape legislation is a part of this – a part of recognising that no rape survivor should have their experience minimised on the basis of their gender.
You’re keen to point out in this post that you consider both rape and sexual assault to be horrible, while reserving for rape one particular definition that excludes any instance not involving a man as the aggressor and a woman as the victim. But it’s disingenuous of you to suggest that differentiating them in such a way is not a big deal – rape, in all but the most exceptional cases, leads to harsher sentences for rapists and greater support for rape survivors than those found in sexual assault cases.
Your attitude towards rape seems old-fashioned to me, based on a common law understanding that evolved before acceptance and understanding of homosexuality, transexuality, queerness or hosts of other things. It is based on an understanding of sex that only considered penis in vagina. It isn’t based on the trauma caused, the use of sex – in all it’s varieties and types – as a weapon, the process of tearing apart consent and enforcing dominance.
I think the difference between rape and sexual assault is less definitive than you think. I think that your desire to reserve the term ‘rape’ for cases of PiV has much less to do with caring for and supporting rape survivors than with becoming another tool for you to use in your campaign of excluding, minimising, denying and despising trans* people. I think that you’re willingness to categorise and place definitions upon rape survivors in the course of furthering your own agenda is morally wrong.
Rape is only ever penis in vagina.