See, I am probably someone that you would all complain about. We don't have much money and in fact never have (burdened by uni debts, expensive rent, not enough wages). We don't want to not go out at, that would be very sad and anti social, so yes, if we go out and only have a main course and soft drink we would rather pay for what we ate.
It's different if I am out with all my good friends, but a work thing or with people where I don't know everyone, we just don't have the cash to splash around.
I remember one incident when I first started my current job, we all went out for someone else's leaving do to TGI fridays (near work). I din't yet know anyone, I had only been there 2 weeks and therefore hadn't been paid yet, haven't just left a temp job. I had a main course and soda a lime and everyone else had at least 2 courses and cocktails. They all wanted to split the bill and I nearly cried, but didn't say anything as I was so new.
A couple of years later the same situation (though I still didn't have any money) and another girl had joined the team. I warned her what happened last time and neither of us having any money (we were both the youngest, everyone else was older and more established) we said to the organiser before hand that we couldn't afford to split the bill. So when the time came she made a really big deal of saying "right we'll split the bill - oh but Bumper and XXXX are just paying for what they had, so everyone else owes XXXX and they are just paying for their own" making us feel very small and very embarrassed.