I'm not surprised at all. HPUX is not GNU/Linux. The GNU tools are much more flexible and built to overcome the limitations found in many standard UNIX tools.

As an example, I remember using ls in a directory with many files (>64k, oops) and HP's ls just barfed. Of course GNU's ls has no such problem. If it's optional in the standard, GNU has it but HPUX probably doesn't.

Disclaimer: I haven't run any "big iron" in over 5 years so things may have changed.