[narag]

Not sure if I explained it well. The difference between tú/vosotros y usted/ustedes is the former is informal while the latter is more formal, showing extra respect for the interlocutor. Usted/ustedes uses the same verbal forms as he/she/they, instead of the ones for "you".

The oddity is that this use of "ustedes" (only in plural, not for "usted") uses the verbal form for "you all" instead of the verbal form for "they", so it's weird for people from other parts of the country.

As for the use of "usted" in general, it's declining, specially in urban areas.