Affection in public

Since arriving in Japan back in March, I have noticed, among other things, that couples rarely show affection to each other in public while out and about. While I do occasionally see a young couple holding hands while walking down the street (usually 1/100 instances), it strikes me as odd that there is nothing beyond that. Admittedly, I've been just as guilty of being self conscious about showing affection to my girlfriend in public, and she agrees that it is indeed not a common thing to see around (unless you're hanging by Kamogawa... then again, every couple, foreigner, and person wanting to drink generally hangs by there, so make of that what you will). I'm not sure if this is something that happens in Japan, or if there is a sense of disapproval of showing affection in Asian societies in general.
As a result, it's really hard to tell which ones are actually couples, and which ones are actually just friends hanging out. Especially in light of things I had learned in my Japanese Society class, where various reasons are highlighted on why not as many people get married in Japanese society. Two of the main reasons that I found was money, where the man feels that until he is earning a steady income, he feels he is not ready for marriage (especially when it's expected that men in Japanese society are the sole money earners in the family), combined with the fact that a wedding in Japan can cost quite a bit, with the parents usually chipping in as well. I'm not sure of the exact cost of a Japanese wedding, but it is certainly more than weddings that I have attended in Australia, one being my sister's which was very informal, with a wedding at a church, and everyone just heading back to her house for a buffet style dinner, and that is probably one of the cheaper alternatives I've seen. The other factor I found was just down to general social awkwardness. Hell, even the lecturer was joking about the whole "if you're foreign, you'll being able to meet a Japanese girl without any problems." I never really did believe that, until I started dating a few months ago. I won't go in to details out of respect for my girlfriend, but I'll just say I'm glad I decided not to be meteorologist, because my prediction before I left Australia regarding meeting someone in Japan was completely off.