Kotaku is on there because it's part of the lifehacker/consumerist network. They get some nice linklove from a very powerful site in the eyes of google. If you look at the top blog list you can see that between gizmodo and lifehacker, that boosts inbound for kotaku.
I didn't even know UGO still existed, or cheatcc for that matter. Then there are a few I've never heard of. Yahoo is there for one reason, they are the top result on google for "Video Games." I've never really considered them a source for game information.