I haven't seen that in porn, but it's definitely true that porn often presents sexual acts as non-consensual or not clearly consensual when, in reality, the same things could easily be consensual.
If a couple were doing this in real life, there would be a bunch of ways that they could communicate about consent. Of course the receptive partner could still ignore those forms of communication - which would indeed be sexual assault - but then, that's true of almost any sexual act; you don't need to have someone so obviously pinned down to be able to assault them; and if a person is pinned down because they want to be, then there's nothing wrong about that.
As to whether or how much it actually happens in real life - it's impossible to say. I've never experienced something like that personally, but then that's not very useful to you.
Unfortunately sexual assault statistics don't go into this kind of detail, and even if they did, I suspect that underreporting would make such stats fairly meaningless.
Really, though, although I have no evidence, I think this is a porn thing. A lot of porn doesn't tend to portray some of the rather central elements of healthy sex, in this case the element of both (or all) people taking part enthusiastically and caring about each other's comfort and pleasure (a lot of porn has one actor being the one being pleasured, and the other just sort of being there as a sex toy more than as an equal partner who actually
wants the other to experience pleasure and gets fulfilment from that themselves, which sounds a lot like what you're describing); and also the element of, as you say, discussion, agreement - porn actors are handed a script and told to do those things, the process that others need to go through of finding out what they both like, don't like, want to do, don't want to do etc. is completely missing. That's sad, because it gives the impression that sexual partners are supposed to either just know what to do, or to just do what they want to do and hope the other person is okay with it, like Kaizen's second example, which is very problematic.
A lot of porn also romanticises violence (usually "minor" violence - like pushing someone up against a wall - but not always) and consent violation, which is ick ick ick ick. I find it really really sad that we have a cultural narrative that says that one person (usually a guy in an opposite sex pairing, though not in this example) "taking control" is sexy, because what's a lot sexier is having someone you want to have sex with say "I want to push you up against that wall and kiss you", which integrates the excitement and the dominance (if you're into that, which not as many people are as porn would suggest, but it's still a sizeable chunk of people) and the consent. But alas, porn producers haven't decided to include that in their definition of sexual fantasy yet, so what we get instead is consensually dubious scenes like the ones you've seen.