Well - NOT to be contrary - but the only reason they appear to be more intuitive and/or practical is simply because you are so used to them - don't you think? That's like how a german was once trying to convince me that the german language was the most natural based on the fact that it has natural onomatopoeia - that, for example - the word "fahrzeug" -meaning "airplane" - conjures the image of an airplane immediately. I'd say that's called association.

As for metres/centimetres/millimetres - well - you can deal with that with a floating decimal point, right? Try THAT with SAE.