I'd imagine that broadcasters on national networks like Univision are told to standardize their accents as much as possible and ditch the regional slang in favor of words and phrases understood by all Spanish speakers in this hemisphere.
It is not just slang. Word usage varies in Latin America widely, with the same word having separate regional meanings.
In Puerto Rico, the word to "pick up" or to "hang up" (as in clothes in a closet) is the same as the term for fornication in Mexico.
The word for Bus in Puerto Rico is the word for Baby in Ecuador. The word for waste basket is different in at least 4 areas I have worked or lived in.
This is not a question of accents and slang, it is a question of dialects and even use of verb tenses.
Much as the major English-language networks require their anchors and other announcers to speak "standard" English with a geography-neutral accent -- a national anchor might be from Boston or Brooklyn or Birmingham, but before getting that job he or she will have had to get rid of as much of their native accents as possible.
The "standard accent" is closest to that of Medell?*n, Colombia, as it is a clean, standard Spanish pronounced as per the dictionary and the RAE.
The same issue comes in with movies and TV shows that are dubbed or titled for Latin America. There may be multiple versions, according to the region.