The few extra inches of space are important to some travelers (and likely less important to others), especially on 5-6 hr flights. I know access to E+ is one reason why United over the years has earned a lot of my business as a self-funded leisure traveler. If I chose an AS flight with Premium Class seating, it would likely be for that reason and I would be unhappy if I was given a regular economy seat. AS should do their best to minimize seat reassignment if they want to keep their loyal customers... loyal.