Zander, I don't know where in the UK you are, but if I say such-and-such object is 100 degrees, everyone will assume it is the temperature of boiling water. Perhaps some old pesnioner might not. Everyone under 40 (hey! 99% of the gaming demographic!) will use celsius and look at you funny when you mention Fahrenheit.
Europe has nearly twice the POTENTIAL market of the US, simply because of the larger populaton. That the current market in the US is larger, doesn't mean that you should completely ignore your potential market. I am not saying that Fahrenheit shouldn't be listed int eh DMG, but celsius should MOST definitely be in there. If there is 1 (one, just one!) continental European who used the temperaure rules in the DMG for his arctic/desert campaign for more than 4 sessions, I would be more surprised than hearing 100% infallibel proof that the Pyramids were built by aliens. As spacecraft models.
And Jgbrowning - that link doesn't help at all due to the nature of the Fahrenheit system. Try running an arctic campaign where temperature matters with the Fahrenheit system in the DMG, then converting the temperature every blooming day. I tried it. I decided it was easier to move my campaign 500 miles south on the same continent. Fahrenheit has no, and absolutly no practical basis, unless you grow up with the system. It was a guy who stuck a thermometer up his bum and then decided that that was 100 (and he even did that wrong!), then put another stripe on a completely arbitrary point on the same thermometer and said "That's zero". If there ever comes a reward for success through stupidity, it deserves to go to Fahrenheit postmortum.
Miles? Sure. Feet? Fine. Stones and pounds? Doable. Fahrenheit? ROFLMAO! Yeah, right!
If there is enough market to translate the core books in several different European languages, there is an even larger market for celsius.
Rav