It seems to me that at some point Economy class will be miserable enough that passengers start comparing metrics of service (seat width, seat pitch, etc.) rather than just price and price alone. We just haven't gotten there yet.
I don't fly US domestic routes but for a transoceanic flight it'll typically cost you twice the price of standard economy (and in turn business is about 2x eco+, and first 2x business).
Really? As I recall, Delta and United premium economy are normal economy seats in the forward half of the airplane. It saves you a few minutes deplaning, but does nothing for the comfort level in flight.
On United it is the same economy seat, but it does have more legroom due to increased separation between rows of seats, compared to standard economy.
We have seen it in the past. I remember when JetBlue launched many would take a higher priced seat, for the in flight entertainment. Or Virgin for the service and seat room.