Of course, you have to take into account advertising performance. I don't have any figures to back this up, but I haven't seen any to the contrary so I'm going

Of course, you have to take into account advertising performance. I don't have any figures to back this up, but I haven't seen any to the contrary so I'm going to hypothesise that ads on a really nice site that people enjoy using are going to do better than on a site that's horrible and pisses people off. Plus, the former gives people more spare time to click ads and buy stuff. I don't think the 'more time viewing pages with ads on = more money' is the full story.