You don't say in your post specifically how much your purchase for the item cost you on HSN. If QVC sold it for $6 less than you paid on HSN, maybe there is a reason? I think that might make a difference in perception. I don't find $6 a big ripoff. It's unfortunate, but there might not be a direct comparison to gripe about.
Maybe that one item on HSN was a differrent size or quantity than the item on QVC, justifying the price difference?
Maybe one came with free shipping and not the other?
Maybe the two different price levels were more than two weeks apart or one was a special sale of the day, not the same item at the same day?
They may be sister companies, but if the circumstances or product were different, then the price difference might have a reason. If you clarified what the purchase comparisons actually were, I think you'd get a lot of people to validate your annoyance.