Here is a correction which m akes it exactly 8.0:

  > 987654320 / 123456790
  8.0

I've decremented the numerator and incremented the denominator:

   ( 987654321 - 1 )
   -----------------  = 8
   ( 123456789 + 1 )

Works in other bases. TXR Lisp, base 4:

  1> (/ (poly 4 '(3 2 1)) (poly 4 '(1 2 3)))
  2.11111111111111
  2> (/ (poly 4 '(3 2 0)) (poly 4 '(1 2 4)))
  2.0

It also works for base 2, which is below the lowest base used in the article: the Python code goes from 3.

For base 2, the ratio is 1/1. When we apply the correction, we get (1 - 1) / (1 + 1) = 0, which is 2 - 2.