I don't think nudity is necessary in most movies in which it is shown. From an artistic perspective, I can see it being shown in movies where clones or robots made to imitate humans are made and maybe some other scenarios, but apart from that I don't think it's necessary. Even to highlight a connection between two characters, you can make a steamy or romantic scene without showing any nudity. Then again, I don't have much of an artistic mind so maybe I'm missing something.
Same can be said about excessive violence, but a good action flick will usually have some violence. I find violence more intriguing than nudity in movies. For example, after the second Final Destination movie, all I watched the remaining ones for was the way the deaths would be portrayed.
Again, I don't really have an artistic mind, but to me excessive nudity and violence are something you throw in when you don't have high artistic aspirations and want filler content that you know draws crowds.