I agree that it's reasonable. Consider this C program:

  int main()
  {
    return 4 + 2 + 5 + (19 + 3 * 4) - 8 / 10;
  }

Becomes the following assembly:

    .section    __TEXT,__text,regular,pure_instructions
    .globl  _main
    .align  4, 0x90
  _main:
  Leh_func_begin1:
    pushq   %rbp
  Ltmp0:
    movq    %rsp, %rbp
  Ltmp1:
    movl    $42, -8(%rbp)
    movl    -8(%rbp), %eax
    movl    %eax, -4(%rbp)
    movl    -4(%rbp), %eax
    popq    %rbp
    ret
  Leh_func_end1:

Yes, that's going from "high level" to "low level," but much of the same concepts exist. You have to set up a bunch of stuff unrelated to the computation first, which in the Ruby-to-JavaScript case means setting up the runtime system. In the C-to-assembly case, it means mucking around with the stack. Then the actual computation may not be the most optimal thing, because it was generated by a general framework which can handle any arbitrary computation. Reducing it to something more reasonable looking is an optimization.