At 100kg, I never noticed that I ate more than my 65kg friends, but it still made me feel questionable at a tabehodai.

Then your friends are quite weak, because I know plenty of Japanese people who drink like sponges... my GF among them, she is your average short Japanese lady and yet she can drink twice as much a me o_O

I think you got it the other way; your girlfriend is quite a strong drinker.

Every Asian I've met gets a red face from their first glass of wine. Of course I'm not saying that every Asian must be like that. However it's well known that they're not heavy drinkers (compared to, let's say, an average English, Nordic or Russian drinker).

I think more for liability reasons.

If you tell a male [insert western country] university student on holiday that it's "all you can drink for $20" there's going to be bodies.