I don’t know anyone who does much over 40 hours in the UK, let alone anything close to 80 hours. A few might pick up urgent tasks on the weekend, but only when needed and not regularly.
I think also depends where in the US. In Seattle, a lot of tech workers are with Amazon. When I worked with Amazon, over two years, there were perhaps two weeks total where I worked less than 50 hours. In that job, and in several that followed, the office was for collaboration, meetings, maybe an hour of actual work, and then at home was where the second workday began in a quiet setting & you put in 3-5 hours additional coding (plus whatever on-call threw at you).
I've worked for US companies on their EU offices for nearly 10 years, and there's definitely much less of it here, but I've definitely ran into some US employees who have been less than impressed at how unavailable I am outside hours in that time