>>7,8
I'd agree that making third generic for both vectors and lists is a good idea, while making caddr the same would be stupid.
Terseness is only good up to the point where it remains obvious what something is, and I think lispers/schemers understand this well. I don't think C programmers have a right to engage in a terseness debate when any given C program of around 200 lines could be written in less than 20 lines of Lisp or Scheme with actual semantics. We can hang our hats once an APL programmer shows up.