When using my iPad mini to view weekly calender, the shows nearly fill up the entire screen, which is good except when I am trying to scroll down because I often end up touching near the row of stars (even if I am being careful) and I end up rating a show that I have not seen, or even a show that has not even aired, and end up marking it as watched as well! It is easy to go back and unwatch the show, but once rated it doesn't seem possible to unrate. Sure, I can go back and change the rating once I have seen the show (that's if I remember), but I'm sure some here treat the ratings very seriously and I would hate to skew (or screw) the ratings.
The other answer is not to use the weekly calender with the iPad mini, but one of the main reasons I went for premium was the ability to easily mark my shows as 'watched' using a small tablet. :)