I think if you routing around using seach you can find a petrolum engineers description about the technical differences.
Basicaly from what I remember it start's by coming out of the same tap.
Then one lot gets a load of paper work started on it and batched up and the other goes off down a pipe.
Then they start adding things to it.
Presume the difference in smell's is just the different esters to do with the additives.