I like to commend my American friends for their undying loyalty to the memory of the Empire. U.S. customary units are derived from units that helped the British conquer the world, but even the British themselves have shamelessly abandoned them for the units of a filthy, monarch-less republic. It's good to see that Americans still subconsciously yearn for the firm ruling hand of their rightful Queen.
In case you are not joking... in metric countries we still say the same sentences you say, with miles and inches. That doesn't mean we use the olde units to actually measure something...
Sorry, but no. They are just our old units that stuck in everyday language. They are probably not even closer to yours than yours are to antique Egypt ones, given that they were not internationally standardized and merely referenced the same body parts.
And we have expressions including other old units that you don't have (lieu, arpent, toise, etc.).
Not really --- in some languages these sayings actually are already in metric units. The SI system is by now over hundred years old, so just by waiting probably will upgrade unit system also there.
In Russian you still have people using colloquialisms and idioms with units that were put out of use almost a century ago, yet everyone here gets the meaning (or at least the intent, which is what matters in the contexts they are used in) since they have stayed in the literature written centuries ago and of course nobody went out of their way to fix measurements in works of fiction.
Heck, most people using them don't even have a rough idea of how much they originally meant, and if you were to press them to give you a number for the sake of an experiment, they might be 2 orders of magnitude off.
I think there's a serious point to what you're saying. I was bought up in the UK so I have metres for short distances and miles for long distances. If you say to me 5 miles I instantly know what you mean. If you say 8km, I have an academic understanding but not really an intuitive feel for what you mean (other than 8km=5mi, feel 5mi).
I doubt that in practice an average person would be able to (reasonably) accurately differentiate between 4 miles and 5 miles or 6km and 8km without external measurement tools in an unfamiliar environment.
The heuristics at play that the human brain would use is likely: "5 miles is way more than I'd normally want to walk on my feet, since the trip would take me about 2 hours."
But Brits haven't completely abandoned them, have they? Maybe for educational, scientific and in manufacturing industries it's all metric but they still seem to use a blend of imperial and metric for day to day stuff. The distance is in miles, speed in miles/hr, they use lbs as well and deg.F from time to time (mostly deg.C tho),"pints" for beer, ft and in for height etc.
I was born and raised in the US and I don't think I've ever met someone who has any sort of complex about the British Empire, or who would be any more insulted by "you should be ruled by the Queen" than "you should be ruled by the President of Uruguay" (or any other random country). The US was last part of the British Empire before most of our ancestors came to this country.
Honestly your comment, assuming it is meant to be taken seriously, strikes me as bizarre, and I suspect you're misinterpreting your American friends' reactions.
Note: Americans hate it when I do this.