I saw this article too. When I was at WDW late April/early May of this year, the mug was only one price, $16.49 I believe at Art of Animation. We got them with the DP, but I remember looking and commenting to my husband that the pricing per day must not have worked. I thought the pricing per day was kind of silly and again something Disney was making way too complicated. I'm sure people over and over bought the mug for the incorrect number of days.
Making everything as complicated as possible seems to be a theme with Disney lately. I love Disney, and I'm a lawyer so I don't mind all the crazy rules and regulations. I deal with that kind of stuff on a daily basis. However, many of my friends who like Disney and want to do a once every decade trip find Disney to be too complicated.