Please stop spreading false legal advice. Adding commentary on top of video game footage has not yet been tested in court and has no precident set for it.
Until someone actually takes it to court and forces the issue, we have no protection of any kind. Further to that, the DMCA trumps fair use on YouTube which makes the whole argument about our right to do this useless.
It is plausible that in a true court challenge, just the basic act of moving when, where and how in a video game can be considered intellectual property belonging to the recording individual. It seems far more likely that commentary about the game in a review or walkthrough informational fashion would fall under fair use. It also seems likely that true parody or comedic elements directly related to the game could fall under the same classification. However, the simple act of talking while playing adds so little of value to the original product. The whole point of fair use laws is that the additional value is significant enough as to make it a product in and of itself even though the original song/game/movie was a part of the creation.