Just because you're a CPA doesn't mean you can outwit me with numbers :).
The capacity figure USCHO has on that chart is the old capacity figure. Based on the 5800 capacity, the 2012-13 average attendance was 92.4% of capacity. For 2011-12, the average attendance was 90.4% of capacity, although obviously higher in total per game. You may recall (and Spath had some articles/posts on this at the time) that in the Fall of 2011, there were some poorly attended games, some of which were attributed to a conflict with a late afternoon or evening road fottball game that was on TV.
For 2010-11, USCHO has the Big Chill attendance figures in the average, so you can't really figure out what the average Yost attendance is from their chart.
I would agree that attendance the last 2 years is down from seasons prior to 2010-11, where the average attendance is shown as 99-101% of capacity.