The author seems to be assuming that all operating systems use the same implementation or have the same man page even for these random number generator devices -- they do not.

For example, on Solaris from random(7D):

  The   /dev/random   and /dev/urandom  files  are suitable
  for applications requiring high quality random numbers
  for cryptographic purposes.
  ...
  While bytes produced by  the /dev/urandom  interface are
  of lower quality than bytes produced by /dev/random, they
  are nonetheless suitable for less demanding  and shorter
  term cryptographic uses such as short term session keys,
  paddings, and challenge strings.

In short, on Solaris, you can use either one although you are encouraged to only use /dev/urandom for specific cases.