It seems as though certain owners keep complaining over and over again about their PON being itchy. What would you suggest ?

Those owners need to do their own independent research rather than rely on those who love to rant about their rarified experiences.

Why do certain PONS always get into trouble and chew on their owners clothing ? 

I would tend to look more at the way that owners run their households. Have they "pon-proofed" their homes ?

Why do some owners offer more food during winter months ?

You aren't doing your PON a favor by overfeeding him/her. Extra pounds may lead to serious health issues.

It seems as though more PONS in the USA react to pollen. What is your opinion ?

This may have more to do with planting a wide range of trees and bushes which have generated more pollen activity than with PON immune systems. Consult a specialist for a more detailed response.