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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.
Placement isn't the issue though.
If you recognize it as a legit/real advertisement, that breaks the immersion.
Your mind thinks "Why am I paying money to watch commercials?", and that breaks the immersion of whatever virtual world you're in at the time.
If the game is set in the "real world", an advertisement for a fake brand of a real product is, to me at least, more immersion breaking than it being a real brand for that product. Now if the game isn't set in our world it's a completely different story.
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.