I don't think that is a valid comparison. Why? Because in my experience on US routes, I can get discounted economy much more easily than discounted premium economy.

So AKL-LAX return may be about 2000 in economy, but almost 3500 in premium economy. Cf full business is 7000, discounted can be had (sometimes) for under 5000. In this case 1500 difference for premium economy is way too much IMHO. The business fare is also too much when you can get to europe (twice as far) for the same price - but this is supply and demand at work. So I look for ways to get it cheaper, like scheduling us visits into the same trip as europe, taking RTWs, etc.