Assets are the same from PC low to PC ultra too... but there are more than just resolution differences.
Talking generally, as well as the specific case of the Witcher.
i am now shaken to the core with this interview
We haven’t covered the technical aspects of The Witcher 3 too much. I will quote your statement for Game Industry from March 2013: “PC allows for more at the moment but next-gens are catching up; it will be easier to unify the requirements in the future”. Do you think that the future has already come?
I think so, yes. You cannot develop a game for three platforms that will use all the amazing technical novelties and improvements that are unique for each device. This is a technical fact. Making an exclusive title allows to squeeze out much more from given machine.
You do realize that this interview was done back in January right? That means it was done before a full four months of optimization. Since then (I cannot remember the article and will link it if I can dig it up) the devs have come out and stated that they will stick with these requirements despite the optimization making it so that they could likely lower them. I would say that they shot high with the requirements but that anyone sitting around with a GTX 770 will probably do MUCH better than 30fps on mid-high. This has been a theme I have noticed quite a bit actually, several of the last games I bought had a requirement of a GTX 480 for high and 30fps but with a GTX 570 I was playing on Ultra getting 40fps.