> but you have to admit that the existence of these SLDs (like co.uk)

I'm sorry, what ? Admit ? Confusion ?

In the case of .co.uk it has been around since 1996. HN is a technical forum, most people here should be well aware it is a serious SLD. I honestly can't believe it even needs clarifying.

Hell, if you use AWS Route 53 you'll see they use co.uk as one of their nameserver suffixes[1].

[1] https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/SO...