The fact that Julia made her little quip without thinking is exactly the point.
We once used words like '******', 'spastic', 'darkie', 'Jewboy', 'pansy', 'Chink' as parts of normal speech. We wouldn't bring them out in polite society these days, because we understand that they subtly encapsulate a patronising, derogatory dismissal of a group of people.
We know that now because we have been 'encouraged' to give it some thought.
That's why PC-ness is such a burden - we're forced to think before we speak, when it would be so much easier not to have to do that work.
Much fewer of us would bother, I suspect, if we didn't have a constant example in front of us - the media. People on television are enormously careful in what they say, and gradually the habit sinks into the viewer and eventually we're surprised to hear a nicely spoken person say 'nignog'.
The Irish joke is old and worn out. What's troubling is the fact that, in an attempt to deflect blame, Julia reached for a weapon that should have had many alarm bells ringing in her mind. She's not a drunk slouched in a doorway (yet); she's a media presenter who's being listened to, live, by hundreds of thousands. And, having made an error of judgement, a professional presenter should have apologised properly and fully, which she didn't.
Yes, the entire show disappeared as far as QVC videos were concerned. I would be surprised if Julia didn't spend some time in a manager's office, without tea and biscuits.