Numbers Numbers Everywhere

So why is it some numbers are shown in totally non-logical ways?

Car fuel gauges show 4/4, 2/4 and 0 for Full, Half and Empty.  Why not 1 to 0?  4/4, 2/4, 0/4?  4/4, 1/2, 0?

And analog clocks with Roman numerals have I, II, III and IIII, not I, II, III and IV as you'd expect.

Just stuff I wonder about...