For my american friends, Feliz 4 de julio, Día de la independencia de los Estados Unidos de America!,(a little late, I know haha).
Well, you already have mentioned that "vosotros" (and "sois" and "os", "habéis", "perdonéis") are almost exclusively used in Spain, whereas "ustedes", "son", "les" and "han" can be found more commonly in Latinamerican Spanish (of course most of us understand the meaning of those words, since we sometimes use it in school (literature and philosphy).
And yes! Don Quijote is quite difficult even for us native speakers, first, because it uses an old version of castillian or spanish (from spain) and even if it has been modified to fit the 'new' spain-spanish, they still use for example, vosotros. Also , it is not difficult to find a "latinamerican spanish" version of Don Quijote, (want to know the complete name of this book by Miguel de Saavedra a.k.a the Spanish Shakeaspeare?): "El ingenioso hidalgo don Quijote de La Mancha" "The Ingenious Gentleman Don Quixote of La Mancha" .
"En un lugar de la Mancha, de cuyo nombre no quiero acordarme, no hace mucho tiempo que vivía un hidalgo de los de lanza en astillero, adarga antigua, rocín flaco y galgo corredor." ("In a village of La Mancha, whose name I do not wish to recall, there lived, not very long ago, one of those gentlemen with a lance in the lance-rack, an ancient shield, a skinny old horse, and a fast greyhound.")...
Anyway, back to main subject, If i wanted to "translate" that expression to latin american spanish it would be something like:
"Le ruego que me perdone, Lord Eddard. No ha venido a escuchar recuerdos seniles de un verano olvidado antes de que naciera su padre"
And , yes, it is a formal form, otherwise the sentence would be:
"Te ruego que me perdones, Eddard. No has venido a escuchar recuerdos seniles de un verano olvidado antes de que naciera tu padre"
Notice the little differences? So, we have 3 phrases, that say the exact same thing, but written in a different way.
I hope this helps!
Saludos desde Baja California, México.
P.S Excuse my english, any corrections will be appreciated.