I've seen both the english and swedish versions of the films, I prefer the swedish (but again, think both books and films are vastly overrated, they are just 'alright' in my opinion). I don't really understand why you think the violence and sex is unnecessary to make the plot stand, both are quite critical to Lisbeth Salander's rather mysterious character, she doesn't see violence and sex the same way we would, plus it's all part of turning the female role on its head (as marwel7 touched on). Plus the rape scene in the first film is pretty crucial.
The films reflect the books fairly accurately (all things considered) so why the violence and sex would be acceptable in the books but not the films does rather confuse me.