Hmm its not that hugging is rude but you wouldn't be as touchy with someone you first met? Its totally normal once you get to know someone and couples and friends in Korea are more cuddly than I'm used to in the US!
once my husband kissed me in the train (s.korea) and someone screamed at us and said it was not ok. same sex affection is ok ( but are not gay/bi) but older people dont like to see kissing and touching.
I've heard that Japanese people really respect their privacy and won't do any kind of physical contact in public. I'm not sure about Koreans though.
Off topic a bit but I grew up in Mexico and #5 is so true lol.