One of the benefits in achieving the higher Premier status levels is the benefit of blocking a middle seat next to you. I have had several flights where I have been the highest-ranking UAL flyer only to find the middle seat next to mine is filled. The person was not traveling with the person in the window seat (as I generally get an aisle). Looking around the immediate vicinity, I often see a few middle seats not filled. Upon indiscriminately looking at the manifest, I find that the luck flyers with empty middle seat next to them are lower in Premier level than I am. So what gives here?