What is even worse, is scientific shows like Mythbusters use BOTH systems. Usually they use metric, usually it's F but sometimes it's C. Weighs usually pounds, but they also have used (kilo)grammes. Distance is usually inches and feet, but when bouncing a baseball they were measuring the bounce in cm - while other parts of the same experiment were using inches and feet.
There is no consistency, and that alone can give rise to errors. It doesn't really matter whether one uses cm or inches, or C or F as long as it's consistent. Forget to write down the unit once, and it's guesswork that's left. Have a thermometer with both scales - oops which scale were we using again this time?
You write "(kilo)grammes," so it's possible you're watching it on UK television. The US and Europe (in countries that don't dub or lector) have two different voiceovers, and the European one translates all the US customary figures to metric. It's not as unnatural in the US broadcast.
It's still pretty jarring television; you're right about that.