Actually it probably does a "poor" kid from the right back ground (minor nobility landed gentry or even middle class ) will find it easier to get into Oxbridge / Harvard and also grok the social aspects as your parents told you how it works - Boris Johnson is a good example originally not rich but had a lot of connections.
For example know why not to wear "brown" shoes in town to an interview for a high paying job / internship.
I'm not British, but I've worked for several British companies and this topic has come up in conversation when I complimented someone on their black shoes with a Navy suit, as it's a combination that I never thought to pair (I hate black shoes).
My understanding is brown shoes are considered to be sporty or informal Britons. It's something you'd wear to go hunting or on a picnic, never to a work. So I think wearing brown shoes with business attire is seen almost like an American wearing hiking boots.
Because it shows that you don't know the rule not to wear "brown" shoes in town to an interview for a high paying job / internship and thus are not of the right class to get a high paying job / internship.
Though here perhaps the "class" is not exactly the right word. To know etiquette is not quite the same as belonging to a social class.
Question: do upper class Americans eat with fork in the left hand and knife in the right? Because I notice most everyone in America that I have met eats with the fork in the right hand, and I am almost unable to eat that way (except dessert).
It's curious, as a lot of etiquette norms are grown out of simply practical considerations (in this case, dominant right hand considered safer for knife).
For example know why not to wear "brown" shoes in town to an interview for a high paying job / internship.