I 'believe' they go with a more generic room key in order to be less deluxe vs value minded. I think they want their guests to feel that everyone is valued, that those staying in a deluxe are no more important than those in a value. I'm sure some might feel that if the resort logo was on the room key, and they were staying at POP, that perhaps they wouldn't be looked upon in the same manner as someone with the GF logo on their key card.
It isn't hard to keep cards separate...the dates of each stay are on the bottom of the card. I like the way they do the cards now..it's much less 'class conscious'..if you follow me.