Well with the new upgrade rules for domestic flights, it's cabin booked, then your status, then your million miler status, that dictates your upgrade order. It's no longer a M fare get's the upgrade before a X fare, and your status was always before the type of fare booked regardless so a Diamond would always get upgraded before a Platinum or Gold Medallion. I can't see any logic in why a Platinum regardless of fare class and price would get the upgrade before a Diamond based on how the rest of the structure has worked in the past, nor how it's explained now.