Of course if you wanted to be pedantic, you could argue that since we are talking about fuel consumption we should state it as how much fuel is consumed. So litres goes on the top of the fraction and the distance goes on the bottom. Putting the distance on the top of the fraction whether it is miles or kilometre surely means that whatever the figure describes it is not actually fuel consumption.
The 100 is not an issue. It is only there the give a reasonable degree of accuracy without too many decimal places. I know it involves the same number of significant figures, but 10.5Litres/100km looks neater than .105Litres/km. Anyway working with 10s or 100s is not a big deal. You don't really have to do any maths. Just move the decimal point up or down one or two places.

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1973 Series III LWB 1983 - 2006
1998 300 Tdi Defender Trayback 2006 -
- often fitted with a Trayon slide-on camper.