Publishers who own the IP to titles can claim copyright to the gameplays. Since it is basically free promotion for their games, it's against their best interest. Hence, you see them offering their blessing and support to YouTubers.
They're also attempting to claim copyright on game reviews. Which in short, puts reviewers in a bad position where someone is trying to monetize their opinion and are easily silenced if that opinion is unpopular.
For reviewers its grossly unfair for publishers to make money off their reviews, because while they will reference their game, the opinions expressed are entirely the reviewer's, and writing a critique is certainly nothing at all like showing a dry gameplay video with no commentary or editing.
Sometimes you see the characters using a Mac complete with logo visible and sometimes the logo gets covered.
The reasons for this may also come from both ends. Either Apple can say "We did not authorize the use of our trademark" or they could just enjoy the free exposure on TV. On the other hand, the TV shows producers could say "What we would do with displaying the logo in that way would be advertising, therefore Apple would have to pay us to show their logo. Otherwise we just cover it up"