Because farm animals are inherently good, whereas the Wise Woman are at best neutral: they're willing to buy and sell evil items (like the Dark Helm) and to evil-aligned people.

This isn't D&D, where dumb animals are considered True Neutral; the world of Arcanum follows its own set of rules.

Arcanum seems to be vaguely meant to recall Britain (United Kingdom, , [url=http://en.wikipedia.org/wiki/Durham#Name]Dernholm, Cumbria). The British are known to be a nation of animal lovers. Gypsy lovers, not necessarily.