Addressing the second point first. Try this. Draw a line across a piece of paper. Mark 1/10th of the line. Try again, but mark 1/2, 1/3, and 1/4. Now, draw a short line. Draw another line that is 2x, 3x, and 4x. Repeat and draw a line that is 10x. Unless I'm mistaken, one will find that factors of 2, 3, and 4 are readily visualized, while factors of 10 are not.
Now consider time. The relationship between common units is certainly not decimal. The units are chosen on the question that one wants answered.
The relationships between various imperial measures are typically ratios of 2, 3, and 4. Nothing too exotic. The imperial system provides a wealth of individual measures that are coupled to the scope of whatever is being measured and can easily be scaled upward and downward. The metric system, though, has a sparser set of measures (I will assert that adding prefixes, such as centi- or kilo-, creates a new unit of measure).
The conversion factors between imperial measures are not that complex and the quantity of measures allows selection of units appropriate to the question at hand. Conversion factors only become complex when trying to switch back and forth between imperial and metric.