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, keep a daily journal and switch away from kibble.

Why do certain PONS tend to 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 or do they  leave undergarments available for their PONS to grab and chew.

Why do many 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 such as heart,diabetes,joint problems.

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 then with PON immune systems. Consult a specialist for a more detailed response.