This isn't universal. German is a counter example -- the formal Sie derives from the third person plural, while it still preserves Du and Ihr for informal second person with singular and plural.
I don't know Spanish well, but it probably contradicts this as well. Usted and Ustedes are not related to vosotros (informal second person informal, not used in the Americas) and take the verbs for third person like German.
It's not anything so specific as a group. It's about distancing or impersonalizing the speech. It's too direct to say "Do you want something to drink?" and instead the phrasing could be "Does the gentleman want something to drink?"
We do something similar with phrasing like "if you would like" or in German using subjunctive forms of many verbs like "I would like" / "Ich möchte" / "quisiera" instead of "I want" / "Ich mag" / "quiero".
In Italian, the third person feminine is formal. The first person plural is also formal, but (I believe) it's archaic. So, when speaking formally, one would say "can she help me?" to mean "can you help me?"
I especially didn't mention if it is second or third form because this varies: some languages might have plural form of second ant third person to be the same word.
I agree with your point of distancing and today that is usually the case, because direct confrontation is left for friends. Phrases like "do the gentlemen want ..." or "could she help me ..." are not counter examples: basically by addressing someone indirectly like this one allows ANYONE to respond. Like husband, or one of the gentlemen to collect everyone's orders.
I remember learning that in high school, and things made so much more sense; it explains why usted takes third-person verbs and possessive pronouns.
Wasn't vosotros used as a formal tu at one time, especially with regard to royalty? I seem to recall reading that, but I can't say it with any degree of confidence.
I don't know Spanish well, but it probably contradicts this as well. Usted and Ustedes are not related to vosotros (informal second person informal, not used in the Americas) and take the verbs for third person like German.
It's not anything so specific as a group. It's about distancing or impersonalizing the speech. It's too direct to say "Do you want something to drink?" and instead the phrasing could be "Does the gentleman want something to drink?"
We do something similar with phrasing like "if you would like" or in German using subjunctive forms of many verbs like "I would like" / "Ich möchte" / "quisiera" instead of "I want" / "Ich mag" / "quiero".