Spanish translations made in Spain use "vos" as an archaic substitute of "usted" when the movie or book is ambiented in Middle Ages, Renaissence or those times. There are many movies and theatre works like that, either Spanish or translated.
For example, the translation of The Hobbit to Spanish does that. Also the translation of Robin Hood, by Walter Scott, to Spanish. Or the translations of The Count of Montecristo and also of Travel to the Centre of Earth, by Jules Verne (even though they're ambiented in 19th century, they use all the time "vos" as a substitute of "usted", to translate French "vous"). Also in Quixote, or in the theatre of Lope de Vega and Calderón, we find this kind of treatment as the normal for singular politeness.
My Final Fantasy VI translation uses this for the character CYAN, too. He speaks using "vos" (except in familiar situations, when he uses "tú").
But that "vos", of course, is conjugated with diphthongued verbal forms, that is "sois", "estáis", "hacéis", "venís", "mirabais", "vendríais", "llegaréis", "habéis venido". Same conjugation than for vosotros.
Actually, Argentinian "vos" uses "vosotros" conjugation in an archaic, monophthongued variety (sos, recordás, hacés, podés, venís, estabas, vendrías) that co-existed with other forms (like sodes, soes, sois) in written standard Spanish until XV century. That monophthongued form became eventually less frequent, but remained in Spain until XVI. Time enough so this form of conjugation passed to the Americas, where it became dominant in some regions like Argentina, probably even for "vosotros" itself, even for plural.
Other archaic form of this vos/vosotros conjugation was finished in -des (sodes, cantades, queredes, tenedes, venides, estábades, vendríades), that evolved into modern -is (sois, cantáis, queréis, tenéis, venís, estabais, vendríais) towards XV/XVI centuries.
I put you an example with this excerpt from a XV century romance poem (I add some of the previous verses for context):
« Rodillada está Moriana,
que la quieren degollar,
con sus ojos envendados
non cesando de llorar,
atada de pies y manos,
que era lástima mirar;
los cabellos de oro puro
que al suelo quieren llegar
y sus pechos descubiertos,
más blancos que non cristal.
En viendo el verdugo moro
en ella tanta beldad,
de su amor estando preso
sin poderlo más celar,
fablóle en algarabía,
como a aquella que la sabe:
que mandado soy, señora,
por el rey moro Galván.
Ojalá viese mi alma
cómo vos poder librar
para liberar dos vidas
que aquí las veo penar."
Morïana dijo: "¡Moro,
lo que te quiero rogar
es que cumplas con tu oficio
sin un punto más tardar!"
Al tiempo de la su muerte
éstas voces fue a fablar:
"Yo muero como cristiana,
y también sin confesar
los pecados verdaderos
de mi esposo natural."»
Kneeling is Morïana,
they want her throat to be cut,
with her eyes that were blindfolded
not ceasing at all to cry,
her hands and feet have been tied,
that made who watched to feel sad;
her hair, made of so pure gold,
the floor is wanting to touch,
and her breasts have got uncovered,
they're whiter than even glass.
By seeing the moor executioner
in her so beautiful sight,
being imprisoned by her love,
he can't his jealousy stand.
He spoke to her in good Arabic
like if she were to understand:
"Ye must forgive me, Moriana,
I hope ye want to forgive,
since I am receiving orders
from the Moorish king Morian.
If only my soul could see
how to be able to free ye,
in order to free two lives
that here I'm seeing them in pain."
Morïana told him: "Moor!
What I beg thee and request
is to accomplish thy task
with no other slight delay!"
In the moment of her death
these voices she was to claim:
"I'll die today as a Christian,
but without having confessed
the true sins towards my husband,
my only legitimate."
Anyway there are regions of America where that modern colloquial "vos", that replaces "tú" instead "usted", is conjugated with diphthongued forms, too, like in Spain, and in standard Spanish grammar. An example of this is Maracaibo region, in Venezuela (¿vos estáis contento?).
Another thing that is not right in your saying: you speak as if using that colloquial "vos" was something from the whole of American Spanish. That's not like that at all. Colloquial "Vos" is not shared by the whole Hispanic America. Actually many Hispanic American countries don't use "vos" at all, like Mexico (except Chiapas), Peru, Cuba, Dominican Republic, Puerto Rico, most of Venezuela, most of Colombia, and others.
That's why the only form of standard familiar treatment in Hispanic America is "tú", as in Spain. That's what we call "general Spanish", or standard grammar and vocabulary, as opposed to "regional Spanish" (like in Argentina or Uruguay).
Example of a sentence in general and in regional Spanish:
Lo que me cuentas es extraordinario.
(Meaning: what you tell me is awesome)
Esa vaina está bien arrecha (Venezuela)
Es re-loco lo que me contás
Me estoy quedando hela'o, quillo (Seville, southern Spain)
Acabas por hastiarme, muchacho.
(Meaning: you end up spending my patience, boy)
Ya párale con esa vaina, chamo (Venezuela)
Me estás cargando, loco (Argentina)
Me estás poniendo la cabeza como un bombo, primo (Seville)