The British are big on buying rounds. In my experience, when you go to a [pub] with British folk, they beeline it for the bar, collecting orders from the group on the way. It's almost that they delight in starting off the evening by picking up the first round. People in London don't drive a lot, so it must be like their version of yelling "shotgun!" in the parking lot. Whatever it is, the act feels genuine, and without need of reciprocation.
But there's some unspoken co-op strategy to this round-buying idea. Perhaps something like this: everyone's going to drink the number of beers equal to, or greater than, the number in the group. So the number of people you go out with is directly proportional to the level of your anticipated drunkenness. Five people in the group = five beer night. Six people = six beer night. Note: I'm not sure if martinis or pina coladas apply in this situation. Also note: I've never seen a pina colada ordered in a British [pub].
My friends are just discovering this round-buying concept, and it's making everyone's life a little better. The waiter/waitress/bartender doesn't have to run [insert number of group members] credit cards, and we don't have to wait for the waiter/waitress/bartender to do so. Plus, some trips to the bar are 'free.'
So why the change from an 'everyone for themselves' approach? I've come to a conclusion based on plain economics: five years into our adult working life, we have more money. Plus, it's fun. You feel like a hero in knowing that you're treating. When you buy a round of drinks, you're in a scene that reminds everyone of Cheers rerun.
Once I have enough extra cash blowing around, I'm going to walk into a bar and stand up on a stool and announce, "next round's on me!" I imagine that there will be cheering, some shouting. Ted Dansen might be there with a pre-White Men Can't Jump Woody Harrelson. Confetti might drop on the crowd, and everyone will want to shake my hand. In the uproar, they'll ask for my name, and what part of England I'm from.