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Gamers enraged at Ubisoft for injecting ads into the middle of video games
(www.techspot.com)
This is a most excellent place for technology news and articles.
The thing though is that the real advertisement will remind you that you paid money to watch a commercial, and that's where the immersion breaking happens.
With a fake ad you know you didn't pay real money to some other real human being somewhere else, and that your purchase went just for the recreational value of the game you're playing.
In other words, it's not the content of the ad, but the realization that it's a real ad, regardless of it's content, that's immersion-breaking.