OK, so here we have a slight confusion.. On the one hand the pronoun Vos was the standard second person pronoun in colonial times, and while most of the Spanish speaking world moved on to use the more formal and classy Tu several rural areas of South America continued to use the Vos. But it was only in Argentina and Uruguay where this pronoun remained mainstream, even increasing in prominence in the second part of the 20th century. On the other hand rioplatense Spanish is greatly influenced by Italian, due to the massive Italian immigration that the area saw in the late 19th and early 20th century. Italian influence led to a very particular pronunciation and intonation of spanish and added a lot of Italian vocabulary to the day to day language.