This seems to be a generational and geographical gap. Speaking parochially, among relatively well-off 40-ish Australians acting like this would mark you as some kind of cheapskate space alien.

I remember being similarly surprised at the 'down to the last penny' bill-splitting when I first got to the US, but, as a lot of people remark on in other threads, many of the social gatherings weren't really very long term (e.g. a random collection of Bell Labs interns).

I'm sure that there are good reasons people act this way, but the impression that I have to fight down when someone acts like this that you're either cheap, broke or paranoid about being taken advantage of. I think there are occasions where everyone needs to get a little more fine-grained (especially not doing the thing where non-drinkers subsidize drinkers) but the amount of time some people fritter away on these calculations makes me wonder what their time is worth...