People who live in the real world (ie they do not work in IT and are not French) prefer imperial as it is easier to understand and visualise what they mean. For example, when I am guaging someone's running speed outside I will tell them to hold 8 minute/mile pace whilst running or go out and cycle 25 miles. If I say to run at 12.9km/h I would get a blank look.
That is nothing to do with the intrinsic merits of either system, but rather, what people are used to. The UK and the US still use a mix of (mostly) Imperial and metric (as you know, kCal is a metricated unit itself, defined in terms of kilogrammes and degrees centigrade/celsius and Watts and Joules are also metric) but most other countries use metric. In my opinion, though, most British people under about 40 don't know how many yards or feet there are in a mile (and, frankly, their estimates of how far a mile actually is are often completely bizarre) and may not even know how many pounds are in a stone (or ounces in a pound; in fact, the ounce as a unit of measurement is less used than it was even when I was a kid). Miles per Hour is probably about the most significant measurement in Imperial that people really do use a lot, but then, only really when applied to vehicles (in my experience, people in the UK are not so good at judging walking or running speeds in miles per hour unless they are actually runners). Problems with km <--> miles conversions, and I agree with you that they exist, are a sad indictment of the average arithmetical ability in the UK, as a good approximate conversion from miles <--> kilometers is easy.
I would think that Bill Gates, as a nerd, will probably enforce metric, except that it will be given a new code name. And if he's bitter about anyone giving him a hard time, it would be the US Government, rather than that of the EU.
British people would look less stupid if we didn't dig in our heels against the French when the French and nearly everyone else are clearly 100% right. I bet the ancestors of gribble and Ictus were railing against the newfangled Arabic numerals when there was nothing wrong with good old traditional Roman numerals.