Hi Dotta, you may be right!
It has always hit me as disrespectful, though. I would say further that the family never refers to her by Kate, at least not in recent years, and isn't it polite to use what seems to be the preference for that person? She would be deemed rude to correct people, but there hasn't been any indication that the grown woman, now wife of the heir to the thrown, wants to be called by a nickname.
Still, as I said, your perspective may be closer to truth than mine. It's just always rubbed me the wrong way. (Thank heavens her nickname wasn't Kitty!)