It's basically what you would call a trailer. They downsized when us kids left home and bought that when they retired. It's worth less than their car. They are by no means middle class.
Maybe the saying should be reversed then!
Probably so. I'd also ponder when the saying came about. Pre-EU? Pre-tunnel to France?
Without science, I could see that a portion of US or UK population travels a lot and a portion doesn't. And each portion might be large enough to seem like it "covers everybody" if that's all you talk to.
And I know for some people, mobility has increased. My in-laws raised 4 kids and probably never left the state of WI. Once the mom-in-law got a degree (when my wife went to college), and all her kids moved out, they were off to Florida, Hawaii, even visited us in TX. Now, the mom-in-law's been to New Zealand and NY even. That's a crazy shift from staying put to getting out. largely influenced by money and family restrictions.
We've gotten very off track. Sorry. I have heard that UK/EU folks are highly mobile across countries (thanks to the UK) likely due to the EU open border thing. I am sure there are fuddy-duddies like me though, who "no, we can't nip off to XYZ-land, for reasons..."