When you get past everything (and considering my comments in other threads) it occurs to me that the general standard for when something goes from "erotic" to "pornographic" is when you actually show penetration. Indeed this is the standard used in the US for when something goes from "R" to "X" and in part why so many "R" rated movies can have far more intense seeming sexual content than ones that actually get an "X" rating, actually seeing "Piece 1 go into Piece 2" is the thing. With the anal probe, you actually see it slide up someone's butt, and in the abortion scene there is penetration with the vac. Abortion also has the baggage of being an international political issue and that content is pretty much an affront to both sides, which I'm sure applied, but probably wasn't the deciding factor.
That's my guess of course, I beat the game and I can't think of any other scenes where any kind of sexual penetration is actually shown, though one scene
shrinking and climbing up Mr. Slave's ass and finding all of the sex toys and spirits of dead animals lodged in there, some of which feature in puzzles to proceed
comes very close, though it's not traditional penetration in a sexual sense, so I imagine it got a pass for that reason. Even the whole
scene of your parents having wild sex, followed by a shrunken fight on their bed where you dodge, and eventually get crushed by your father's swinging scrotum
doesn't go past "R" rated material since simply showing a sex organ, and people playing "naked twister" generally doesn't go past "R".
That said, the game is pretty good, it actually did a decent job of recycling their old gags (which you expect in a South Park product) and creating new ones. From the looks of things it seems primed for there to be more DLC adventures so we'll see what happens in the long term with their content and censorship. Honestly I'd be all for one that seriously knocks Europe and Australia and sets new precedents for sick content in the process... in part because of the censorship, and partially because they have arguably flogged Canada enough.