I'm in London and every 4 minutes isn't far off. I live in suburbia like most people and can walk 10 minutes to a high street where there and multiple routes at 8 min frequency each way, which overlap for large parts of their route, therefore some journeys really do have a bus every 3 minutes. And if it's a journey from central London to central London then there's going to be 2+ routes that serve every journey.