Depends on the entire structure of the site, and no not only porn sites. If you run chrome, hit up your Network Inspector in the dev tools and go to YouTube (or RedTube if you want, it's just about the same) to watch a video. The random video I had in my chrome history loaded from o-o.preferred.nuq04s10.v21.lscache3.c.youtube.com , and all images loaded from *.ytimg.com

If Youtube were to go down and I tossed their IP address into my hostfile, I could visit their homepage, but there's a pretty good chance thumbnail images wouldn't load, and a 100% chance I would not have every single (seemingly dynamic) content server in my hostfile, so none of the videos would load anyways.