In the workplace some places expect you to take your jacket off and roll up your sleeves. You're not working hard enough if you don't. Other countries expect you to have sleeves unrolled and tie nice and straight, otherwise you're a sloppy worker.
I can definitely see someone (but not me) paying a small amount for that kind of information - the cultural notes you need when visiting some other nation.
Etiquette rules are often the same. Why stand for the "Hallelujah" chorus? Because that's the done thing. Why do people in the US eat with the fork inverted from the way used in the UK? Why is port always passed to the left in the UK, and how is the Bishop of Norwich involved?
The real answer is two-fold. Knowing these practices indicate the you are a member of a certain group. By not knowing them you can feel like an outsider. If there really are a set of easily-learned rules to follow, then you can make the transition to that group. (Jumping back to Element of Style; follow these rules to become a better writer.)
But only rarely is there a simple set of rules to follow - like if you were to meet the Queen of England. It takes years to learn the little rules that a given subgroup acquired over decades, not the few weeks these classes usually do. Plus, etiquette classes usually promote etiquette rules specific to a certain style of upper-class culture, and direct their marketing to people of lower social/economic class. The end result is that they encourage a feeling of vague anxiety and nervousness in their target audience, and perhaps also a sense of superiority in those in the upper-class who learned these rules growing up.
The other fold is that there are some bad things which are easily avoided with preparation. Don't wear orange at a big, rowdy St. Patrick's Day party in Boston unless you're itching for a fight. Those especially occur when mixing very different cultures; eg, in part of the world "Chopsticks should not be left standing vertically in a bowl of rice or other food" because they have a funeral connotation. Cultural awareness training for this case, especially for people moving overseas to a radically different culture, can be very fruitful.
However, as the original poster said "carry themselves properly", I presume the courses are of the first fold - promotion of certain economically upper-class practices - and not the second - avoiding culture clashes.
In any case, it isn't a matter of learning rules before you can break them. It's a matter of learning specific rules in order to appeal to those who believe that those rules are meaningful, whether it be an editor who rejects ".. or less" as valid English, or a person who thinks only buffoons wear white after Labor Day. With that in mind, "carry themselves properly" is not longer absolute but only meaningful if you want to get something from that subgroup of people.