Cordelia's belief that a glass of champagne will harm the developing Miles in Barrayar is the result of superstitious fears due to her lack of familiarity with in vivo pregnancy.
Why are the nobles of Barrayar referred to as the Vor class when 'Vor' is Russian (Which is one of the four common tongues of Barrayar) for 'Thief'? The Vor class started out as the Emperor's tax collectors, who often had to collect taxes at swordpoint during the Time of Isolation. From the perspective of the commoners being shaken down for taxes, they probably looked like thieves.
In the denouement of Komarr, pay attention to which conspirators believe Miles' warning that their MacGuffin is fatally flawed and will not work as originally intended, and which do not. You'll note that the less technically educated the conspirator is, the less willing they are to believe Miles' warning that the thing will just blow up in their faces. The Komarran conspirators' relative degree of caution about Murphy and Finagle are in direct proportion to their amount of experience as engineers!
A cultural reason for the rise of the Vor on Barrayar: The majority of immigrants were stated to be from Britain, France, Russia and Greece, countries which all have some form of noble tradition, so it would be quite easy for them to adapt to a renewed feudal state.