Why is she moaning and sighing so much? He barely even touches her until half way through. [EDIT: <--- wondering about the bath scene in the Youtube Wither 2 video.]
Anyway, games are always going to follow a completely unrealistic, fantasy concept of sex/relationships. Witcher aims for the straight male ideal of being big and strong and hot women will swoon and offer you sex, no strings attached. More realistic is that 60% would be too young/married/old/pregnant etc, 30% would be scared sh*tless/not interested/not wanting to be used and you get your choice of the last 10%. How many of those are young and gorgeous, during the implied medieval setting? Well, probably not that many.
Then again, DA isn't all that realistic either, but the fact that you have people who aren't interested in you, like Vivienne, or people who have set gender/race preferences does help. Also the age range is quite a nice point.
It all just depends on exactly how much fantasy fulfilment you want in your games. For me, DA:i has hit a good enough balance, though I do wish there were more options to flirt with characters and get knocked back or more chances for NPC's to flirt with you so you can accept/reject them.