When you phrase it that way, of course it sounds useless.
Have you ever gone out to a bar and bought a round of drinks for your friends? Yes, that's like $90 a round for 10 people in a New York bar. But I bet you got a drink back from every one of those people some day (and if you didn't, they're not great friends or you make a lot more money than them).
It's kind of the same principle here. It doesn't have to be a steak dinner for 20 people - I know I can't afford that. But if you go out for wings and beer, buy around of beers. If you don't want to do that, go to the local bakery and bring in two dozen bagels and cream cheese. The point isn't how much you spend to be impress everyone, the point is to do something other than just show up and mooch.
Patrick said "Buy your team dinner". That's what I was referring to. Buying a round of drinks is a very different thing, IMO. It's perfectly natural and social behaviour in many cultures.
Note, not trying to be cynical here. Maybe I'm so ingrained with this culture you describe that I can't see your point.