I think it just depends, though you may be right that this "regimented life" is more common in the US. For myself, I'm happy to jump out in the middle of the day if a friend wants to go on an impromptu walk. But if I am planning a get-together at my house with more than a couple people, I probably will send out a calendar invitation. Not because I think the other people need it, but I do like to put things on my calendar so I don't forget when things are going on, and it's only a couple extra seconds to add the guests to it, so I might as well.
As another data point, I know people who are introverted and need a little mental preparation before seeing people, even good friends, so impromptu meetings can cause social anxiety.
> You can call a friend the same day and enjoy a cold beer after work (some time after work, punctuality not required)
I've definitely been trying to get better at the last part of this. People finish work at different times some days, sure. So it's fine to just head to the bar whenever you're done, and whoever gets there first will grab a table and just chill alone with a drink until the other person shows up, and that's the norm, not the exception. But I feel like most of the time (where I live) you try to figure out when both people will be done with work and then only meet when you can arrive at about the same time, creating unnecessary anxiety around punctuality.