Bland name products and Captain Ersatz

[32bit-RedMage]

I am merely asking out of curiosity, since it's always bothered me.

In most cartoons, comics, movies , tv shows and webcomics bland name products and
captain ersatz characters are used instead of real brand names, e.g, Caca-Cola instead of Coca-cola or Mike Jaxon instead of Michael jackson.

Then there are some who DO use real brand names.
Just take a look at family guy.
Family guy refers to movies, games, actors etc. by their real names.

Is that legal? Don't they get sued for that, and if it is legal why does everyone else not use real names and brands ?

As far as I know it is forbidden to use real logos, but I've seen some Tv-shows use 'em anyway...

Does anybody know what's up with all this?