"Sexual assault" of a 17 year old man by a mid-30s female teacher 
Would it be any different if it were a 17 year old woman and her 30 year old teacher? When I was 17 I wanted to fuck my teachers sometimes.
I don't think there's any difference here, honestly.
You're correct. Both should be viewed as sexual assault, but a lot of straight men think with their dicks on "OH A HOT OLDER WOMAN WANTED TO SCREW ME WHEN I WAS A KID" as a fantasy.
And before someone starts: No, I'd say the same shit for same-sex. It's assault no matter how you want to define it under the law. You want to bang an 18 year old at 40? Fine, I may not approve of the age difference, but that's lawful under the law. Don't be screwing any 17 year and under kids.